Spam.abuse.net, by Scott Hazen Mueller, provider of the graphics on these pages.
The Coalition Against Unsolicited Commercial Email (CAUCE)
The Network Abuse Clearinghouse, intended to help the Internet community to report and control network abuse and abusive users.
Netizens Against Gratuitous Spamming (NAGS), another good resource, by Ian Leicht. With pages called Mission Statement, Bite Back, Case Studies, Mail Filter, Internet Resrouces, and NAGS News.
SpamHelp.org, with collections of anti-spam software, hardware-based appliances, news, articles, books, and events. Very cool.
Spam Pages from Get Netwise, sponsored and run by an impressive list of dot-com and dot-org outfits. With tips, tools, and action assistance.