You know what collective nouns are-- like a gaggle of geese, or a swarm of bees. I've reprinted David's list below the jump, and I have to say, some of it is genius: "a blush of Blood Elves," "a den of rogues," and a "congregation of priests" are definitely my favorites. But there is some room for improvement-- "an annoyance of gnomes" is funny, but couldn't there be a better word for that? Maybe a "short stack"?
And there have got to be better things to call a group of Alliance and a group of Horde, so post your own ideas in the comments below. I have to say, though, "a murder of Murlocs" is just about perfect. Don't touch that one.