My Friday favorite is SpamSieve. We have mentioned it a few times previously, but since it has recently been updated to version 2.76 I wanted to sing its praises again. It's the best way I've found to deal with spam.
Using Bayesian filtering, SpamSieve installs as a plug-in to your mail client and lets you mark messages as spam. As you do, it builds a a corpus file of rules telling determining what is spam and what isn't. The more messages you mark, or train, the more accurate SpamSieve gets. I've been using it since November of 2003 and after years of training, it's so accurate that it rarely fails to catch an errant spam encrusted message. When it does, using either a keystroke sequence or a pulldown menu from your Mail client you can train it as spam.
At the start, it's quite labor intensive since you have to mark a few hundred messages for it to really start working, but it pays dividends. After a while, you'll have a personalized set of inclusion/exclusion rules that gets better over time. To give you an idea, yesterday I received 307 emails. Out of those SpamSieve correctly marked and moved over 30 messages and missed only 2 that needed training.