I'm using CA Anti-Spam blocker and its the best by far. it scans your sent list and approves those people right away. then you can adjust the levels of what you want to block. then every time something new comes in it will list them and you can approve the ones that are good. it keeps them all in a folder so you can go in and check just to make sure before deleting them. after a week or so it's letting only what you want through and the one or 2 new ones that come in are easy to approve or block. i haven't had any problems with it and for $30 you can put it on 3 PC's .. check it out
http://shop.ca.com/spam/spam_blocker.aspx