Science and Pseudoscience
Most of the works recommended here are not very difficult or technical.
They should be understandable even if you have little science background.
Ian Stewart, The Story of Mathematics 
A comprehensive and very readable survey of the entire field, from ancient times to the 21st century.
Tobias Dantzig, Number, the Language of Science
Good introductory exposition of the nature and development of mathematics.
E.T. Bell, Men of Mathematics
Short biographies of the greatest mathematicians of the past.
James R. Newman (ed.), The World of Mathematics (4 vols.)
Excellent collection of the literature of mathematics over the ages articles on different areas of mathematics, historical vignettes, biographical sketches, philosophical ramifications. Most of the pieces assume some elementary mathematical awareness, but not much more.
Clifton Fadiman (ed.), Fantasia Mathematica; The Mathematical Magpie
Two lighter collections of essays, short stories, humor, fantasy, puzzles, etc., selected by the well-known literary critic.
Edwin Abbott, Flatland
A popular Victorian-era story about a visit to a world that has two dimensions instead of three. For a lively sequel, written more than a century later, see Ian Stewarts Flatterland — a wild ride through the wildest concepts of modern mathematics (topology, fractals, multiple dimensions, etc.).
Martin Gardner, Aha! Insight; Aha! Gotcha
Gardner is well known for his numerous collections of mathematical games and puzzles drawn from his Scientific American columns. Those collections may sometimes be a bit too specialized for nonmath people, but the two Aha! books are easily understandable by anybody. They require no mathematical background, only an open and alert mind.
Raymond Smullyan, What Is the Name of This Book?
Smullyan is a magician, a musician, a mathematician, a logician, and a delightful writer. What Is the Name of This Book? is a series of logical puzzles and paradoxes in various fantasy settings (e.g. an island where some people always tell the truth and others always lie). Smullyan has written several other similar books, including Alices Adventures in Puzzleland and The Riddle of Scheherazade. If you are a chess player, try his The Chess Mysteries of Sherlock Holmes.
Douglas Hofstadter, Gödel, Escher, Bach
If you like Smullyan, this immense metaphysical fugue in the spirit of Lewis Carroll offers much more about similar and related topics, examined with a similarly wry humor, including delightful dialogical interludes by Achilles and the Tortoise dramatizing the ramifications of infinity, self-reference paradoxes, etc., as well as their connections with computers and the mind.
PHYSICS AND ASTRONOMY
Martin Gardner, The Relativity Explosion 
There have been several popular introductions to relativity, including one by Einstein himself and another by Bertrand Russell, but Gardners is probably the best.
Heinz Pagels, The Cosmic Code
Of the many recent books that attempt to explain quantum physics to the layperson, this is one of the best.
Richard Feynman [1918-1988]
Besides being a renowned physicist, Richard Feynman was an amusing character and a delightful writer. There are numerous collections of his popular lectures (many on videotape as well as in print form). Six Easy Pieces is the most accessible; some of the others may be rather challenging if you are not already pretty familiar with science and math. His two autobiographical volumes Surely Youre Joking, Mr. Feynman! and What Do You Care What Other People Think? can be understood and enjoyed by anyone.
A Brief History of Time 
Recent findings and speculations on the cutting edge of physics and cosmology, from the Big Bang to black holes. There are several books about Hawking and his ideas, partly due to the significance of his work, partly due to the intriguing fact that he accomplished it despite being almost totally paralyzed.
Brian Greene, The Fabric of the Cosmos
This book ties together the topics of the above four books, giving the latest discoveries and speculations about how relativity and quantum physics can be reconciled, the ultimate nature of space and time, etc. A lot of it is pretty mind-boggling, to say the least.
Timothy Ferris, Galaxies
The history, nature, forms and varieties of galaxies, illustrated with 143 superb photos. The latter make this a fine coffee-table book.
Incidentally, the first thing I do after starting my computer in the morning is check out the Astronomy Picture of the Day. Each day it presents a new photo, with a professional astronomer’s brief explanation of whatever the image is about. A nice way to start the day by putting earthly affairs in a very broad perspective.
Asimov has written numerous excellent books on physics and astronomy Understanding Physics, Asimov on Physics, Asimov on Astronomy, Asimovs Guide to Earth and Space, The Universe: From Flat Earth to Quasar, Exploring the Earth and the Cosmos, etc. See the ISAAC ASIMOV section below.
Charles Darwin, The Origin of Species 
One of the most important books ever written. It is thorough and meticulous, but not all that difficult. (Darwin lived in the era when scientists still knew how to write readable prose and addressed their works to the general public, not merely to their fellow professionals.) The followup volume, The Descent of Man, though historically more controversial due to its subject, is less crucial since it simply applies the same types of arguments to human evolution.
Stephen Jay Gould [1941-2002]
Gould manages to convey relatively sophisticated points without speaking down to his readers. Of his twenty or so books, ten are collections of his monthly essays on the odd, fascinating and endlessly variegated byways of natural history and evolution, with titles such as The Pandas Thumb, Hens Teeth and Horses Toes, The Flamingos Smile, Bully for Brontosaurus, Eight Little Piggies, and Dinosaur in a Haystack. All are highly recommended.
Richard Dawkins, Climbing Mount Improbable
Illuminating explanations of seemingly problematic aspects of evolution, such as how did something so complicated as the eye evolve?
Jean-Henri Fabre, The Insect World of J. Henri Fabre
Selections from the great French entomologist, noted for his patient observation and genial style.
Jane Goodall, In the Shadow of Man; Through a Window: My Thirty Years with
the Chimpanzees of Gombe [1971, 1990]
These two volumes, the first reporting on Goodalls first decade of research, the second looking back twenty years later, recount one of the most fascinating and exemplary scientific ventures of the twentieth century.
Donald Johanson and Maitland Edey, Lucy: The Beginnings of Humankind
First-hand account of the discovery of the famous hominid skeleton, with a good general discussion of its implications for the various theories of early human evolution.
Lewis Thomas [1913-1993]
Thomas wrote several volumes of interesting essays, primarily on biology and medicine, but branching off at times into psychology, language, and other social and cultural issues.
John Muir, My First Summer in the Sierra
By the great outdoorsman, initiator of the national parks program and inspirer of Rexroth, Gary Snyder, and countless other explorers of the California mountains. I recommend the slightly abridged edition entitled Gentle Wilderness, which is illustrated with superb photos of the places and things Muir is writing about. If you like this sort of thing you may also enjoy Muirs other books, The Yosemite and The Mountains of California.
[Rexroth guidebook, Camping in the Western Mountains]
Aldo Leopold, Sand County Almanac
Quiet observations of nature in the tradition of Thoreau and Gilbert White. This book was a major influence on the development of an ecological ethic.
Isaac Asimov and Frederik Pohl, Our Angry Earth
Although written long ago, this remains an excellent account of the continually increasing threats to the global ecology. There have been numerous books that examine one or another environmental problem, but this is one of the few that consider the situation and its possible solutions as a whole.
Isaac Asimov (1920-1992) is the greatest ever popularizer of science, bar none. A few others, such as Carl Sagan or Martin Gardner or Stephen Jay Gould, may have written a few better books in their particular fields, but Asimov covered virtually every area so lucidly that almost anyone should be able to understand just about any of his writings. And he did this not in a few dozen books, but in nearly 500! Admittedly, many of them are very short volumes for children, or anthologies that he merely edited; but that still leaves well over 200 real books.
Ive read more than a hundred of them. Ive never been very excited by Asimovs science fiction, but I love his nonfiction. My favorites are the 27 volumes collected from the monthly science articles he wrote for The Magazine of Fantasy and Science Fiction. These are mixed bags of essays on any scientific topic that appealed to him at the moment, always put across with a light touch What would a sunset look like from one of Jupiters moons? What would sex be like in a zero-gravity space station? Since they were directed to regular science-fiction readers, they tend to be slightly more chatty and freewheeling than some of his other works of popularization (he doesnt have to stop and explain that the earth goes around the sun). There is a one-volume selection of these essays entitled Asimov on Science: A Thirty-Year Retrospective.
He wrote numerous other books that systematically explore general areas of science (astronomy, physics, chemistry, biology) or some specific topic (novas, black holes, atomic particles, DNA, etc.).
He also wrote on a variety of nonscience topics Asimovs Guide to the Bible, Asimovs Guide to Shakespeare, Isaac Asimovs Treasury of Humor, annotated editions of Gullivers Travels, Byrons Don Juan, and Gilbert and Sullivan, a couple dozen volumes of history, and three volumes of autobiography.
When his publisher urged him to write an autobiography he at first shied away from the idea, protesting that when you write hundreds of books, what time do you have for an adventurous life that people would want to read about? Eventually he gave in and wrote a huge two-volume narrative. I remember checking out the first volume, thinking that its 700+ pages would keep me occupied for quite a while. Three days later I had to go back to the library to get the second volume. Yet apart from a few amusing anecdotes about the science-fiction scene, theres not much out of the ordinary that happens in it. I dont know how he does it, but somehow he has a knack of making anything he writes about both informative and entertaining. For me, Rexroth is the only writer who can match him in this respect. Perhaps this is because both of them had so thoroughly assimilated the things they wrote about that they could rattle off an essay without needing to do much research or rewriting, making it seem effortless and conversational.
There are far too many excellent Asimov books to list individually. I can only suggest that you browse the Asimov titles in your local library catalog for whatever topics interest you.
As an experiment, someone advertised himself as an astrologer in a major newspaper. Several hundred people sent him their birth dates. He sent each of them a horoscope, along with a form letter asking them to let him know how accurate they found it. More than 90% responded that the horoscope showed astonishingly accurate insights into their particular personalities and problems. In reality, he had sent every one of them the same horoscope.
Some people will say, So what? Astrology and things like that are just harmless entertainment, like getting your fortune told at a county fair. Unfortunately, irrational beliefs are not always so harmless. Countless people, for example, have died because they trusted themselves to faith healers or psychic surgeons instead of seeking proper medical treatment. But more generally, if people are incapable of seeing through the most crude paranormal cons, they are likely to be just as gullible when it comes to judging social and political questions.
Its an uphill battle. Publishers and mass media tend to promote the most sensationalistic material because it sells, whereas skeptical refutations are ignored or relegated to the background. (And now heres our token sound bite by one of those boring arrogant scientists with closed minds. . . .)
But lest I sound too grim, let me assure you that the following works are highly entertaining. The shrewd investigative work of people like Joe Nickell is as intriguing as a good detective story. It is both fascinating and gratifying to see how James Randi manages to expose a renowned psychic or faith healer as a con man. And it is amusing (though also sad) to learn how gullible most people are, and how they will continue to cling to the most ridiculous and discredited beliefs rather than admit that someone has made a fool of them.
[Rexroth article on pseudoscience]
James Randi, Flim-Flam! Psychics, ESP, Unicorns and Other Delusions
As a professional magician, James Randi has known how to discover and expose the tricks used by supposed psychics of all kinds. And he has put his money where his mouth is: The Million Dollar Paranormal Challenge is a standing offer of $1,000,000 to anyone who can demonstrate evidence of any paranormal, supernatural, or occult power or event under scientifically controlled conditions. Over the last four decades hundreds of self-proclaimed psychics, clairvoyants, dowsers, aura-viewers, etc., have tried to do so. So far not one has succeeded.
Flim-Flam! is the most comprehensive collection of Randis debunkings. I also recommend his The Faith Healers and The Truth about Uri Geller.
Carl Sagan, The Demon-Haunted World
Carl Sagan was noted for his widely popular books and television programs about astronomy, space travel and the possibilities of extraterrestrial life. In this book, written shortly before his untimely death, he deplores the increasing prevalence of irrationalism and superstition and examines several recent instances. He does this in a more gentle and tactful manner than Randi, making it clear that he realizes that people are drawn to these beliefs through partly legitimate or at least understandable reasons e.g. a justifiable tendency to distrust authorities, or a natural desire to retain a sense of wonder. Regarding the former issue, he shows how science includes more automatic self-questioning and self-testing procedures than any other field of human endeavor. In response to the latter concern, he shows how science continues to reveal far more wonders in the world than the banal sensationalism of paranormal claims.
Kendrick Frazier (ed.), The Skeptical Inquirer
The Skeptical Inquirer is the journal of the Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP), the organization that Isaac Asimov called an island of sanity in a sea of nonsense. It has been appearing since 1976, and is by far the most important international forum for news and commentary on purported paranormal phenomena. Frazier has also edited several anthologies of selections from the journal: Paranormal Borderlands of Science; Science Confronts the Paranormal; The Hundredth Monkey and Other Paradigms of the Paranormal; Encounters with the Paranormal.
Martin Gardner, Fads and Fallacies in the Name of Science; Science: Good,
Bad, and Bogus [1957, 1981]
Fads and Fallacies, a ground-breaking work of skeptical inquiry published back in the 1950s, is a fascinating account of the Flat Earth Society, Velikovskian astronomy, Atlantis cultists, Pyramidology, Dianetics (Scientology), Lysenkoism, Reichian orgone boxes, and the search for Bridey Murphy. Gardners later book, Science: Good, Bad and Bogus, examines ESP, psychokinesis, faith healing, precognition, psychic surgery, etc., as well as various fringe-science topics areas that are serious science but where findings remain questionable (e.g. chimpanzees use of sign language) or where scientific concepts are widely misunderstood and misinterpreted (e.g. quantum physics).
M. Lamar Keene, The Psychic Mafia
A former professional psychic reveals some of the tricks of the trade that enable these con men to seem to know things they could not possibly have known unless they were really psychic, raking in huge amounts of money from their gullible clients.
Joe Nickell, Real-Life X-Files: Investigating the Paranormal
The latest collection by the former private detective who has turned his skills to the investigation of supposedly unexplainable phenomena, from poltergeists and haunted houses to crop circles and the Shroud of Turin.
Kendrick Frazier et al. (ed.), The UFO Invasion
Anthology of articles explaining the realities behind UFO sightings, the supposed Roswell coverup, alien abductions, the alien autopsy film, etc.
John Allen Paulos, Innumeracy: Mathematical Illiteracy and Its
Pauloss book isnt exactly about pseudoscience, but the widespread innumeracy he discusses (notably peoples ignorance of how statistics and probability work) is one of the factors that make people susceptible to being fooled by fallacious statements of all kinds (e.g. misjudging how likely some coincidence is, or being panicked by some media-generated bogey while ignoring other problems that represent a thousand times more actual risk). Paulos elaborates on the same theme is his subsequent volumes, Beyond Numeracy and A Mathematician Reads the Newspaper.
Section from Gateway to the Vast Realms (Ken Knabb, 2004).