Depending on what hours you play, there are several active shells I could recommend you to. Some to look into that are both more casual with a mix of end-game are:

Ass Kickers Anonymous
Phoenix Order (very, very late night shell 9pm pst - 1am)
Omen (International shell that has a very strong Asian group)

There are also some more "hardcore" shells that are out there, but I think the above are great places to start. If you're actually interested in PO, please feel free to send me a tell in-game.

P.S. There are also probably some Melmond shells that merged over, but I'm not very knowledgeable on those groups.