"SpamSieve gives you back your inbox by bringing powerful Bayesian spam filtering to Mac e-mail clients. It’s quick and easy to control SpamSieve from within your mail client, and you can customize how it interacts with the rest of your message sorting rules. Other spam filters get worse over time as spammers adapt to their rules; SpamSieve actually gets better over time as it adapts to your mail. By learning from the very messages that you receive, SpamSieve is able to block nearly all of your spam, without putting your good messages in the spam mailbox."
Works like a charm. Spam comes in, but goes away with one click.