Zen Flesh, Zen Bones, compiled by Paul Reps and Nyogen Senzaki (North Clarendon, VT: Tuttle Publishing, 2008), is a brief, accessible introduction to Zen Buddhism.
Zen Classics: Formative Texts in the History of Zen Buddhism by Steven Heine (New York: Oxford University Press USA, 2005) is a scholarly text.
Garden Digest is a well-organized website of Zen fundamentals, including ethical precepts and philosophical tenets.
Find a large collection of koans on at the AshidaKim website.
Looking for Zen garden supplies? Try Buddha Statues Now for an array of items and meditation supplies.
The Dalai Lama website offers a translation of Eight Verses for Training the Mind, with lovely elaboration and explanation.
The pamphlet, Faith of a UU Buddhist, is available from the UUA Bookstore. The author, James Ishmael Ford, also wrote In This Very Moment: A Simple Guide to Zen Buddhism.