When I was a kid, any scifi book from Robert Heinlein or similar authors was an eye opener that made me look past the standard assumed limits that I knew growing up.
Any number of books by Robert Anson Wilson expanded and warped my view of the universe.
More recent books like "the tipping point" "Gonzo marketting" and "cluetrain manifesto" have opened my eyes to other ways of thinking (not just outside the box, but eliminating the box entirely).
Holdem Poker for Advanced players by David Sklansky and Mason Malmuth has also opened my eyes
Alex