Zen Mind, Beginners Mind, by Shunryu Suzuki. These dharma talks by the founder of the San Francisco Zen Center are related in simple style, yet still manage to convey the deeper meanings of Zen and its practice.
Taking the Path of Zen, by Robert Aitken. This is possibly the best nuts-and-bolts book on sitting practice, rituals and form, walking meditation, koan study.
Every Day Zen, by Charlotte Joko Beck. Founder of the American Zen school of Ordinary Mind, Joko speaks in a way easily understandable to the western mind, with especially good advice on sitting practice and relations between people.
Returning to Silence: Zen Practice in Daily Life, by Dainin Katagiri. Offers a basic understanding of Zen Buddhism with a special emphasis on discovering the experience of enlightenment in the midst of everyday life.