Books that Changed Your Life?

Pubb asks: "I'm a Computer Science teacher at a school with an interesting tradition. Every year, the graduating student who has performed best in a particular subject area is given a book prize. Rather than give this particular student the usual book on Java or Linux, I would like to get something more impactful. I ask you, fellow Slashdot readers, to name the books that helped unleash your geek within. All I ask is that the book be reasonably available, even if it is no longer in print."