AngryPets.com: ReverseDOS - A free tool by Michael Campbell to stop comment and referrer spam by serving up an access denied response to spammer's bots.
ILoveJackDaniels.com: Block Referrer Spam - Dave Child provides a blacklist of spamming sites which can be used in an .htaccess file on an Apache server to block referrer spam. (September 14, 2005)
Wired: When the Spam Hits the Blogs - Strange things are afoot in blogland. Owners of weblogs have recently noticed that their referral logs have become the newest target for spam. (October 26, 2002)