I’ve heard a lot about SpamCop recently, and after reading this mefi thread I decided to sign up.
In short, it’s a free service aimed at stopping spam.
When you sign up, you are given a unique email address. Each time you receive spam you just forward the email as an attachment to SpamCop and they take it from there. I don’t know how effective they are, but at least it gives me the feeling that I’m helping to fight in the war against spam.