kittle

Something I found a while back that works well - "bounce"

not all email programs have this feature, but I use a web based email from my ISP and in the rules setup there is "delete message" and "bounce".
So instead of just accepting all the spam thats sent to my emailbox, the rule will bounce back the unwanted stuff. Granted this causes some legit emails to be returned as undeliverable, but I found the benifits well worth the small hassle of having to maintain my own "whitelist" for people who send me email.

I had the same problem as wilthorn did a while back, but boucing everything back made a world of difference.