sorry for not saying games that i've finished and have no intention of playing again
rdr saints row series gta series mass effect series two worlds series dead rising series mafia 2 crackdown 2 oblivion splinter cell conviction alpha protocol borderlands tales of vesperia resonance of fate
The L4D2 community is very active. Just be careful if you play the multiplayer by yourself, 'cause like any other multiplayer game, there's an abundance of idiots and rednecks, and a combination of both. So try and make friends with some competent players and play with them.
Xbox Live GT: Black Mesa Inc & Steam ID: JoeBeef Reading isn't hard if you don't sweat comprehension.
Earth Defense Force: Insect Armageddon. Came out most places on July 5 (some GS stores released it on July 2), so the online should be pretty active (don't know personally...no internet to 360...*sad face*). It's only co-op though, not vs. matches. Here's a trailer:
http://www.amazon.com/shops/A258UKMK08DSV0 Playing: GBA- Final Fantasy V / PSP- Valkyria Chronicles 2, Dynasty Warriors vol. 2 / 360- EDF: Insect Armageddon