ZIGGY29  SpamSieve is the best consumer-grade, easy-to-use spam filter I've ever used, bar none. I've done system/network administration on Unix, Mac and Windows systems, and for the end-user there is simply not a better spam filter I've ever seen. Once trained, it catches well over 99% of the spam and virtually never records a false positive.

I've compared the spam filters in both Apple Mail and Microsoft Entourage, and while both of those are competent (though sometimes lacking), SpamSieve just gets better and better at identifying and quarantining spam as you use it more.

At the $20 price point it would be even more compelling. But for those of us who would get dozens of spams day after day, every day, the $30 price point is still worthwhile in terms of reduced aggravation and lost productivity dealing with massive waves of junk e-mail.   
(Version 2.7.2)