I highly recommend:
D. T. Suzuki, An Introduction to Zen Buddhism, with a forward by Carl Jung.
A collection of Suzuki's essays. Some are more interesting than others. Don't let the "introduction" in the title fool you, this is a deeply philosophical book.
A more devotional kind of read (page-a-day sort of thing):
The Gateless Gate: The Classic Book of Zen Koans, translated with commentary by Koun Yamada.
In addition to the works of Japanese poet, Basho (The Narrow Road to the Deep North and other Travel Sketches) , my favorite book of haiku is The Moon in the Pines, Jonathan Clements, translator, with lovely artwork from The Art Institute of Chicago. Neither the koans or the poetry are "modern".
Shambhala Publications has numerous excellent modern resources. See also publications from the University of Hawaii.
