I'm playing in 4 here, running 3 in real life, and playing in 5 more on another site!
What other site? I have had a hard time finding other sites like this one.
Mythweavers is very good. Board Game Geek does PBP/PBF also. Others I know of are Rolegate (not my cuppa tea) and RPG Crossing. But my favs are here, BGG and Mythweavers.
The only other one I know about that I'd add to that list is Tavern Keeper. I've played for a pretty long time at Myth-Weavers, but they have a very strict PG-13 policy for games, so we came here to do some horror.
Lots of nice people over at RPG Crossing. But they have an even stricter PG-13 policy than MW. That doesn't matter to most people or most of my games, but when it matters, it matters.