For example, off the top of my head, I'd probably recommend "The Selfish Gene" by Dawkins and "The Demon-Haunted World" by Sagan. (I recall enjoying Eldridge's book on punctuated equilibrium, too, but it was years ago, and I was an evolution geek at the time--not sure if that's easily accessible or if it was dense and dull and my memory is just playing tricks on me.) "Flight of the Iguana and other essays in Natural History" was also nifty, and while dated now, you still can't beat Desmond Morris and "The Naked Ape" and "The Human Zoo" which I feel oughta be required reading as a sort've owner's manual for the human body, and the out of print, occasionally wildly speculative, but riveting book "The Sex Contract: The Evolution of Human Behavior" by Helen Fisher, which is nice to have on hand whenever somebody tries to tell you that monogamy is unnatural, look at the bonobos, so you wanna swing, baby? (In addition to it's scientific weight, the hardcover edition can be used to bash the heads of the aforementioned.)
Heck, doesn't neccesarily have to be science, so much as nonfiction--"How the Irish Saved Civilization" was pretty neat reading, too.
So hey, any others?