Bookshelf -- Math Puzzles & Games by Michael Holt

This is a nice little book. A good collection of puzzles concluding with an excellent set of games such as nine men's morris and tactix. It's also another example of the cheap but deserving books Barnes and Noble used to find and republish. They've shut down that division but it's still worth seeking the imprints out when you're in a used book store.

Archimedes' Revenge

Archimedes' Revenge by Paul Hoffman

It's been a few years since I read this but it made a good impression on me at the time and a few of the sections (on voting paradoxes, cryptography and topology, particularly the role it played in the side effects of thalidomide). I'm not sure how well the computer science section holds up, but it's definitely worth a look.