Some good books on the subject:
. Diamond Sutra and Sutra of Hui-Neng - The Diamond Sutra is the oldest extant printed book in the world. Hui-Neng is regarded as the father of the Zen tradition.
. Zen Flesh, Zen Bones - 4 books in 1 covering Zen and pre-Zen thinking over 4000 years
. Siddhartha - A short novel by Hermann Hesse
. Zen Mind, Beginner's Mind - Introduction to Zen practice by Shunryu Suzuki