Ishmael is probably the book that influenced my life the most at the time I read it, and changed my worldview the most. As arebelspy mentioned in his post in the other thread, I'd be curious to reread it now and see how my thoughts have changed. The notion seems more and more simplistic the more often I revisit it (in conversation with somebody else who's read it, maybe), but I'd want to really reread it and not dismiss it based on that impression.
The Holy by the same author remains one of my favorite books.