Looking for a good multiplayer game. Need help. (PC & 360)

I've been getting a little bored with what I got right now so I was hoping for some suggestions from you guys. Need more games though for 360 cuz I got PC down pretty good, but all suggestions are nice. I love multiplayer games and they keep me occupied and sane for many hours lol. Here's what I got atm: 
 
- Counter-Strike: Source 
- Team Fortress 2 
- Killing Floor 
- Modern Warfare 2 
- Quake Wars 
- Lord of the Rings Online 
- Battlefield 2142 
- City of Heroes 
- Supreme Commander

Wait for Battlefield: Bad Company 2, Bioshock 2 and go buy Red Faction: Guerrilla

Halo 3 ODST!

i would wait for bad company 2, which you can get for either system.  
bioshock 2 has multiplayer, but i have a feeling that it wont be a focus. the singleplayer aspect is the one people will care about in that game and the developers probably know it.  
and if you want a cheap fun multiplayer game right now, i would go for battlefield 1943.  its only an arcade game, but sooo fun.

Yeah, as others have said, wait it out for BFBC2. Supposedly, the demo should be released on XBL sometime next week, so that could hold you over until release. Alternatively, you could download BF1943 to tide you over (saying that over BC1 because it might be too similar) and get you ready for BC2.
   
Battlefield is the best multiplayer franchise in my opinion, so I don't think you'll go wrong with that route.

" @FireBurger:  Yea Battlefield games are top notch action for sure. I looove Battlefield 2142 but my disc is super fucked up so I can't really play it anymore which saddens me. But yea I think I might check out BF1943. "

Glad I could help. I tried it with a BF2CC key that I bought from cdkeysdirect a while back, and it worked fine. Such websites are mainly for providing Australian gamers with reasonably priced games (which cost $90+ in retail on average), but many of the prices are lower than the US counterparts (BF2CC was 30 from EA but less than 15 from these sites). Kinda like a freelance Steam, since Steam is key based also.
 
I'd activate all my EA keys, except BF2CC was the only one I owned that I didn't already buy from EADM.
 
edit: looks like ozcdkeys.com went out of business. The site now forwards to Steam.

get left 4 dead 2, pretty good online game.