I've previously mentioned the dilemma of twitter spam. Today I found a really useful website from a friend's blog: Twitblock.org
Here's how it works:
You simply allow it to log into your Twitter account, then it scans your account for potential spammers. It gives them a score (higher score=more likely to be a spammer). Once the suspicious profiles are found, you can either delete them leave them as your followers.
It works pretty well. I ran it and got rid of some pretty nasty profiles. It did pick up a few "false positives" (legitimate profiles), but I just left those alone.