Here's a list of books I recommend about evolution:
On the Evidence for Evolution
Books that show why Evolution is true.
1. Why Evolution Is True by Jerry Coyne. This is a magnificent book that gives several highly convincing lines of evidence to show that Evolution is true.
2. The Greatest Show on Earth: The Evidence for Evolution by Richard Dawkins. Another excellent work that presents the evidence for evolution (albeit with some different evidences than the last book). Especially interesting is Dawkins' replies to creationist canards about the lack of transitional fossils.
3. The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution by Sean Carroll. A fascinating book on genetics and Evolution. I think it does a better job of explaining Natural Selection than the other two books, as well.
Defending Evolution from Creationist Attacks.
1. The Counter-Creationism Handbook by Mark Isaak. An excellent book that provides brief (and well researched) responses to nearly every creationist claim ever made.
2. Evolution vs. Creationism: An Introduction by Eugenie Scott. This book presents creationist arguments (usually in their own words from their own writings) followed by a scientific response.
3. Finding Darwin's God by Ken Miller. This is a very good and very unique response to classic creationism as well as the ID movement.
4. Intelligent Thought: Science versus the Intelligent Design Movement Edited by John Brockman. An intriguing collection of articles that will teach you a lot about evolution and more generally how to respond to intelligent design.
Learning About Evolution
Once you've seen that evolution is true and that creationism is false, you'll probably discover that evolution is fascinating and want to learn more about it. Here are some books to help you out there:
1. The Selfish Gene by Richard Dawkins. A classic book with lucid chapters on the origin of life, the evolution of altruism, and "memes".
2. Life Ascending: The Ten Great Inventions of Evolution by Nick Lane. I'll be honest: A couple of chapters are boring. Still, this is an excellent read explaining how several complicated and very cool things evolved. And yes, creationists, there is a chapter on the eye.
3. At the Water's Edge : Fish with Fingers, Whales with Legs, and How Life Came Ashore but Then Went Back to Sea by Carl Zimmer. Look at the title of the book and tell me you don't want to read it.
4. The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution by Richard Dawkins. A massive book that treks through the entire evolution of life, from modern man all the way back to the primordial soup.
BONUS: Material on the Web that supports evolution.