The Lucifer Principle: Pretty interesting book about the nature of "good" and "evil".
The Bell Curve: Discusses the relationship between social standing and intelligence. A little dry at points, but interesting reading.
The Discoverers: Really good book that talks about the invention of time-keeping devices, the exploration of the world, etc. There's a few other books by the same author in the same vein, but this is the only one I've read so far.