What's in Your Spam-Fighting Arsenal?

Spamhunter asksL "Everyone has their favorite tools to stop spam at the inbox, whether it's using a scoring tool like SpamAssassin, bayesian filters, or something as extreme as challenge/response whitelists (which creates a few problems itself). What I'd like to know is, what are your tools for actively investigating and shutting down spammers? I've found information sites like SPEWS and Spamhaus to be invaluable in tracking down spam gangs and spam-friendly ISP's in order to put pressure where it belongs. Sometimes just chasing the chain of ownership in WHOIS is helpful. What tools, approaches, and resources do you find helpful?"