I've already pretty much left TF2, as I'm currently bored of it, and I'm sure I'll be leaving Bad Company 2 for Brink.
I also recently found the multiplayer in Call of Juarez: Bound in Blood. It's not great, but it's fairly fun. I got the game as part of a bundle a while ago, and didn't even know it had multiplayer until a few days ago. It was a nice surprise, and should help me keep sane until Brink arrives, just because it's somewhat different than most other shooters.