Seeing as no-one has posted any good geology books, I'll recommend some of my favourites...
The Fossil Trail, Ian Tattersall - an excellent summation of Human evolution, a little bit out of date now.
Trilobite, Richard Fortey - how he makes a whole book about small arthropods interesting, I have no idea, but it is a fascinating read.
Global Tectonics, Keary and Vine - everything you ever wanted to know about plate tectonics. More of a textbook than a popular science book, but very readable.
Potential Theory in Gravity & Magnetic Applications, Blakely - this book got me through some of the trickier bits of my Geophysics degree. Explains complicated ideas very well.