Price: Free (donations accepted)

Works with: Apple Mail

Pros: Bayesian filter; regular expressions; wide variety of actions available for suspected spam.

Cons: Complex UI; no universal binary version; nearly two years since last update.

In my testing, JunkMatcher has been extremely effective. The addition of keyboard shortcuts would be welcome, but otherwise it integrates well with Mail. Although less-sophisticated users may be put off by the range of tweakable options, if you’re a geek who likes to tinker, you’ll love the fact that you can mess with JunkMatcher’s settings to your heart’s content. (For that matter, it’s open-source, so you can alter anything you want if you’re so inclined.)

My one big concern: JunkMatcher hasn’t been updated in almost two years, and there’s still no universal binary (though it runs fine under Rosetta on Intel-based Macs). But since it’s free, you have little to lose.