The Fight Against Spam (Score 1)

If you use full headers on your email, you should be able to pull the senders IP address from the header of the spam in question. With that you can go to http://combat.uxn.com. This site will do a Whois query on the IP and return to you the name of the ISP. You can then send a complaint directly to the spammers ISP abuse@.com

I've already had a few accounts blasted after receiving an atrocious amount of spam from their account, and I haven't had a problem with spam for about three months now.