[cliff p.]

In our experience, using GlowHost Spam-O-Matic seems to do the trick. We also signed up for the keys for both spam databases.

In addition, a register time check function helps (ensuring that filling out the registration form takes longer than 25 seconds).

We also use moderation tweaks that look for suspect words in posts from new members with less than 20 posts. If any words are detected, the user is automatically placed into a moderation queue, which makes cleanup VERY easy.