Visions Of Infinity by Ian Stewart (2013, ISBN 978-0-465-02240-3). Subtitled-- The Great Mathematical Problems. I like books about Infinity, however as the subtitle might suggest this book isn't so much about Infinity as it is about various math problems that mathematicians have struggled with over the centuries. Even though it isn't much about Infinity it is still very good.
Some of the problems discussed are Goldbach Conjecture, Squaring the Circle, Four Color Theorem, Kepler Conjecture, Mordell Conjecture, Fermat's Last Theorem, etc. This book is aimed at the general reader, however, the subject is complex and so may be a harder read depending on the reader's math background and interests. The author does a good job of explaining the problems and the attempts to solve them. Purchased from Powell's books on 7-6-2013 for $26.99.