elynne, I have found a Professor Snape pervery community that you don't already belong to!
There is a Sims community at thesims, but it's far too busy for me to read, especially as a quick glance through the first few pages didn't show anything that's not on the TSR forums.
latin is kinda depressing. Not much traffic, and mainly people asking how to translate specific, not very complicated, phrases. latinitas is better in that its userinfo page is all in Latin, but there are only 6 members and no recent posts :(
anxietypanic may be useful for some people. chronicfear and medicalphobia would also be useful if they were busier - but you need to get more members to make them busier, and thus you run into chicken-and-egg...
I suppose people already know about craftgrrl?
Finally, I should plug rhythm_action, just because it's mine.