Zen Koans
Wikipedia: Koan
http://en.wikipedia.org/wiki/Kōan
Understanding the meaning of Zen Koans
http://www.essortment.com/all/zenkoanspiritu_rlmp.htm
Zen Koans
http://www.ashidakim.com/zenkoans/zenindex.html
Zen Koans: Transcending Duality
http://www.chinapage.com/zen/koan1.html
Zen Koans and Haiku
http://www.viewonbuddhism.org/resources/zen_poems.html
The Gateless Gate
http://www.ibiblio.org/zen/cgi-bin/koan-index.pl
Zen Koans
http://awesnob.com/zen/
Zen Koan Database
http://cincinato.org/koans/list_en.php
Zen Buddhism Koan Study Pages
http://www.ciolek.com/WWWVLPages/ZenPages/KoanStudy.html