SpamBouncer has been great for me, and I have it set never to automaticially toss mail. It filters my mail into three folders, Bulk, Blocked, and Spam. Bulk is where any mail not directly addressed to me, plus it fell through all my filters. Blocked is where possible spam goes, but it also sees quite a bit of my new unfiltered listservs. Not a huge problem as a quick procmail edit fixes that. And then Spam, that is where I have only had 5 legitimate messages go out of thousands that have hit it. With Bulk, usually it means it's time for a filter. Blocked gets a quick check once in a while to delete the junk, and Spam gets scanned from time to time before deleting it.

If your someone who dosen't run their own mail server, but know your ISP runs a Unix based OS, see if they can implement it with header additions. Before I switched to IMAP mail, I had Spamblocker adding a simple header that my mail program could pick up on.