I just wanted to post a little rave for Michael Gruber. I have read four of his books so far: The Book of Air and Shadows, The Forgery of Venus, The Good Son, and Tropic of Night.
They are extremely engaging, well written, *amazingly* well-researched, and integrate very interesting discussions around religion, philosophy, the nature of reality, psychology. I just love them.
If you're a more traditional fiction lover, I'd recommend The Good Son. It's a pretty straightforward story, but still includes some mind-opening (at least for me) discussions around religion.
The Book of Air and Shadows I don't remember as well, but it might not be his best since it didn't make as much of an impression.
The Forgery of Venus is a wild mind-bender and also includes some amazing historical detail around Renaissance painting.
Tropic of Night is the one I just finished. And while I don't usually enjoy books with a supernatural element, this one was done with just enough 'science' to make it enjoyable for me.
That's all - just had to get that out there