The various APAs I've been a member of:
Mordred :the first I was ever part of, long defunct. This was a general RPG one.
Comicopia: my baby, still going strong.
APAcalypse: RPG APA. I was a founding member, but I left more than 2 years ago when it became an electronic/PDF thing. I don't know if it still exists.
I have an answer below.Rogues Gallery: A HERO Games APA. When I joined Aaron Allston was the DM. Stephen R. Long took over, but with him now in charge of DOJ (the folks who resurrected HERO) I don't know if the APA is still around.
Now for the others out there. I know there are a few (one of my friends is a member of
Klordny, a Legion of Superheroes APA). Share them here!