I'm reading Richard Dawkins' The Selfish Gene. It's been sitting on my shelf for a year so I'm finally getting to it.
This isn't the first book of his that I've read, and I'm again reminded of how much I really love his writing. He writes in such a clear and manageable way that makes you feel like you're really understanding the material but without sacrificing much in the way of depth. It's a rather rare feat in science writing, in my experience. His fame as a science popularizer is well earned, IMO.
I'm not too far along but it's hard to put down. Pretty impressive, I think, for a 40 year old science book!