I was thinking about that idea as well; setting up some sort of Gang of Five guild, or just meeting for an online game.
The problem I've found, from people I've talked to personally about the idea, is that our interests in games don't match very closely.
I'd be in for the following games (All on the PC. I don't have X-Box Live or anything similar):
Unreal Tournament (the original, 1999 version)
Unreal Tournament 2004
Command and Conquer: Red Alert 2
Quake 2 (don't have quake 3 and I can't run quake 4)
Diablo
Diablo 2 / Expansion
Turok 2: Seeds of Evil
Age of Empires 2
Need for Speed: High Stakes
Need for Speed: Porsche Unleashed
Need for Speed: Hot Pursuit
Need for Speed: Underground 2
4x4 Evolution (1 or 2)
Those are basically all of the online games I own. I don't play many games, as you can see, but I'd be in for any of those.