The Complete Sherlock Holmes stories, A C Doyle. I've read them maybe 3 times in my life. After about a 10-year interval, I find that I can't remember how each story ends, so it's just like reading them for the first time.

The Adventures of Huckleberry Finn, by Mark Twain. I read it 2 or 3 times as a kid. (Along with Tom Sawyer.) I didn't realize it then, but the edition I had was an edited, somewhat dumbed-down child's version. In spite of that, the book was wonderful. I remember feeling really depressed when I came to the end of the book, just because I didn't want it to end. I recently read the original version, and enjoyed it almost as much as I did as a kid. But this time I appreciated Twain's use of language a lot more. I've also read all of Mark Twain's short stories, essays and sketches, and a couple of his travel books.

Among modern novels, I recommend The Quincunx, by Charles Palliser, and Waterland, by Graham Swift.

In the realm of history, I loved the series called The Americans by Daniel Boorstin.

Various articles and essays by Robert Ingersoll. They helped me cut loose from that old time religion. A lot like The Age of Reason by Tom Paine, but by the time I read that, it was almost redundant.

Psychotherapy East and West, by Alan Watts. It tied together a bunch of ideas I had been gathering from other books by other writers, and put religion in a better perspective.

Any book by Idries Shah. I've read everything by him I can get my hands on, and I get more out of them each time I read them. I can't even tell you what they're about. They work on my unconscious mind. It's the closest thing I have to a religion right now.

I'll second Gödel, Escher, Bach. Can't say as it really changed my thinking about anything, though. It's more about the esthetics of complexity.