Yep, an IM app especially designed for gamers. It's called XFire. You can get it at
www.xfire.com
It's got all kinds of cool features, like showing you what games your buddies are in, allowing you to join them, and even shows what the ping is for each buddy who's in a game. You can even use it while you're playing a game. It's still just a beta though - version 0.6.
My username for it is (surprise!) endobioticchaos. It allows only lowercase letters and 0-9.