Take a look at
http://www.spamcop.net

There's a free service where you can forward your spam email to
spamcop@spamcop.net.
The service examines the headers of the message and assembles a report
that you can send to the administrators/anti-abuse coordinators for all
the sites that relayed the message to your box.

I've found it effective.

--
Bradley Flubacher
State College, PA
'84 wasserboxer
'82 diesel westy
'82 diesel vanagon