http://www.spamcop.net/
(Note the .net appendage, and accept no substitutes!)
This site processes spam emails and finds out who to complain to. Once it does that, it's a matter of point-and-click to send out the complaints.
Referrers: http://www.modemac.com/cgi-bin/wiki.pl/30_Minutes_With_the_Lights_Off_(in_Color)/Cast_Iron_Chaos/Modemac/2014-03-03/Cast_Iron_Chaos/Cool_Drug_Stuff_Man/Marijuana_Policy_Project/RecentChanges/The_Devils_Brownies/Cast_Iron_Chaos/Know_Your_Enemy/Net_Scum_Page/Cast_Iron_Chaos/Fun_on_the_Net/Cast_Iron_Chaos/Scumbags_Spammers_and_Scammers