Wohoo... I finally found a good spam "killer" program called POPFile and it's free (GPL), open source and multi-platform.
Installed it couple of days ago and it seems to be working really well. It's kind of a proxy server in between the email client and the email server. The email client talks to the POPFile and the POPFile talks to the email server. Bit of a hassle to set up but if you follow the instructions it should be rather painless to get working (the installer made all the correct settings for me but you still want to double check them).
So here it is: http://popfile.sourceforge.net/