Okay, I just skimmed this thread looking to see if anybody else mentioned this, and I didn't see it. If I am, however, re-recommending a book already mentioned, it's honestly that great and deserves a double-mention. This is the ultimate intro to Zen philosophy, and I have had philosophy professors on both sides of the Atlantic recommend it to classes.
Zen Mind, Beginner's Mind (Paperback)
by Shunryu Suzuki
http://www.amazon.com/gp/product/0834800799