I use a set of procmail filters called Spam Bouncer. It is at http://www.spambouncer.org. Currently, the 2.0 beta is about to become the 2.0 final release, and it is pretty good at catching the spam. It can be run as a normal user, and is actually easiest to run that way. I have fetchmail retrieve my mail, and it does the filtering. It does take some work to set up, but there is a nice sample procmailrc to assist you. I'd actually suggest using the beta because it's more up-to-date. Also, the program does get updated fairly frequently to catch new spammers, etc. It's just another option to consider.
