Cosmos by Carl Sagan. (1980, ISBN 0-394-50294-9) Based on the the 13-part TV series of the same name. That TV series was recently updated with a newer version with Neil deGrasse Tyson. A great book. Contains a lot of interesting stuff, a bit out of date in terms of space exploration (a lot has happened since it was written in 1980.) Still worth reading ( you can find used copies very cheap on Amazon.) I got my copy back in the 1980s.
Contains a proof that the square root of 2 is irrational. Discusses the Googol and the Googolplex. This book contains much information about science and the history of the world, etc.

The Ancestor's Tale by Richard Dawkins. 2004, ISBN 0-618-00583-8.
This is a fantastic book. I loved reading it. (The entry on wikipedia contains a lot of information about the book.) Highly recommended for those interested in learning something about how various living things are related. Since this is a non-fiction science book, information contained in it will change a bit as new discoveries are made, still much of the information is well establish, so this book should be a good introduction to evolution for the layman for many years to come.
Purchased new from the PSU bookstore on 2-23-2005 for $28.