Spambayes. I used to use cloudmark (and even subscribed at $2/month) but it was still letting some through. After a week of training, I maybe get 2 a day which it doesn't filter out.

Yes, I still have to check the "possible spam" folder, but after the first week of training I've not found anything non-spam in there.

Strongly, strongly recommended. spambayes.sourceforge.net I think.

Hugo