I've really enjoyed Zen and the Art of Motorcycle Maintenance and Lila by Robert M. Pirsig.

EDIT: Also, The Phoenix Project is very very good if you are into IT management: funny, and although a novel then the content will make you want to fix your company and perhaps even think bigger about your carrer. But this one won't last you a summer since if you read it that slow you'll forget what was going on. :)