Beautiful Geometry by Eli Maor and Eugen Jost. (2014, ISBN 978-0-691-15099-4.)
51 chapters of interesting mathematics. Each chapter contains one mathematical idea or theorem. Each chapter also contains one or more drawing(s) that illustrate the idea or theorem.
Purchased from Amazon on 1-19-2014, for $20.79

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 Contains a lot of interesting stuff, a bit out of date in terms of space exploration (a lot has happened since it was written in 1980.)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 Universe Within by Neil Shubin (2013, ISBN 978-0-307-47327-1)
Subtitle: The deep history of the human body.
An exploration of human anatomy and how it relates to the evolution of the universe. Another great science book.
Purchased at Powell's 15.95$

Your Inner Fish by Neil Shubin, (2009, ISBN 978-0-307-27745-9)
Subtitle: A journey into the 3.5 billion year history of the human body.
About human anatomy and human evolution. The author is a paleontologist and professor of anatomy. Great science writing, easy to read and very informative.
Purchased at Powell's 16.00$