I know it's kinda old, but I've took a pro-active approach to fighting spam.
The only "filtering" I use is the built-in Gmail filtering (though, from experience, "Windows Mail" filtering in Windows Vista seems fairly decent, surprisingly).
Lately, I've been sending all of my spam e-mail to Knujon.com (yes, they want it all,
knujon@coldrain.net for un-registered users) as well as SpamCop, and more recently, CastleCops.com/SIRT has a Spam fighting service.
SpamCop is only so effective, in this fight more recently, since the spammers seem to be using large botnets of hijacked machines, but Knujon has had quite a success of shutting domains down.