My personal favorite, and one that hasn't been mentioned in this thread yet is the "Bozo Filter" from the Resource Center. It's very similar to Usenet's "killfile" and will surely be appreciated by anyone who's used a newsgroup reader in the past.
For anyone not familiar, here's the summary listed for the hack:
1) registered users place usernames of folks in a list, and posts from that
user will not show up in the thread listings
2) private messages from someone's bozos are blocked
3) when anyone views a bozo's profile they can see how many people have
added this person to their bozo list
4) Anonymous posts may be filtered out
5) users can add other users to their bozo list via a link in the profile
6) anonymous users are not given the personal data of registered users.
Last I checked, the hack worked fairly well, but was a bit inefficient in how it was implemented. I'm hoping Scream decides to pick this one up, clean it up a bit, and make it less intensive.
