Why Evolution is True - Gerry A. Coyne
Not that I needed convincing, but this book, so far, is doing a stellar job of summarizing the preponderance of evidence in support of the theory of evolution, and how said evidence demonstrates conclusively that the theory is sound and testable, no more "in crisis" (as the ID/creationists would have you believe) than the theory of gravity.
It recounts how paleontologists have, over and over again, predicted the existence of certain fossil traits they'd expect to find in fossils of a certain age, only to discover precisely what the theory predicted. How isotope dating has been proven to be accurate by other independent forms of dating.
So even for someone like me who has no doubt of the veracity of Darwin's theories, it's been delightful seeing it laid out in detail, with concrete examples and illustration. It's given me a bit more incite into the particulars of HOW evolutionary scientists have gone about confirming and refining the theory, something about which I've only had vague assumptions.