Understanding Zen

I remember reading Zen and the Art of Motorcycle Maintenance years ago. Here are a few useful books on Zen philosophy.

Manual of Zen Buddhism
http://www.holybooks.com/wp-content/uploads/Manual-of-Zen-Buddhism.pdf
Zen Mind
http://www.arvindguptatoys.com/arvindgupta/zenmind.pdf
The Way of Zen
http://selfdefinition.org/zen/Alan%20Watts%20-%201957%20-%20The%20Way%20of%20Zen.pdf
Basics of Zen Meditation

http://selfdefinition.org/zen/Alan%20Watts%20-%201957%20-%20The%20Way%20of%20Zen.pdf