You sidetracking sonsabitches.

The Selfish Gene - Richard Dawkins
I mean c'mon, read it. Exploration into evolution, altruism, memes etc. employing for example game theory. This is just a massively interesting read.

A Brief History Of Time - Stephen Hawking
Physics, astronomy, time and the universe in a neat and mostly easily approachable package. It's far from a casual read, but considering the subject matter it's quite manageable.

What If?: Serious Scientific Answers to Absurd Hypothetical Questions - Randall Munroe
By the author of xkcd, a bunch of blog posts answering questions sent by readers. If you like xkcd (who doesn't?) and haven't read these, hurry up.