The Tao Is Silent by Raymond Smullyan. I've never been comfortable with traditional Western belief systems. Smullyan's book was the first I had ever read where the philosophy being explored both made sense and appealed to me. He offered a world view in which it was feasible to enjoy one's beliefs...and even not to believe them! Smullyan's musings on good and evil, free will, striving vs acceptance, logic and emotion, the mirror mind, and the happiness of "just being" utterly changed my spiritual outlook.
-- Damian Conway