Here's a new release (April, 2005) with some good ideas! - from Anne Hennegar http://www.timeatlas.com/mos/Reviews/Reports/Guide_to_Controlling_Spam/
1) Visit the Spam Recycling Center and the Network Abuse Clearinghouse for ideas to fight SPAM.
2) Put a few "bot traps" for email-harvesting programs on your web site. The idea is explained at HostedScripts.com site. It's a clever idea: "Email collecting programs will be sent in an infinite loop by following the link at the bottom of the page and will get more and more fake email addresses stuck in their databases." Another similar link is Tower of Babel Anti-Spam
Hey, at this stage, anything helps!