We've got a GTA crew called "Lords of Hucking" who play regular Thursday night sessions (8pm onwards) on PSN/Playstation 3.
Our main focus is on custom capture missions and "story" playlists which use the Creator to make story gameplay for two teams. This gives a good mixture of co-op and competition.
You can see some of our missions here: http://lordsofhucking.wordpress.com/
We have a Twitter feed here: https://twitter.com/lordsofhucking
At the moment we're getting about 8 players a session but want to up this number to keep things interesting.
If you're interested in joining in PM me with your PSN name.