"Alright you new people, after we down Golemagg go run up to the giant rune behind him and take your epic reward."

My fav WoW in-game quote is Ragnaros' speech when someone in your raid is killed: "DIE, INSECT!"

There was a realm forum thread about how WoW quotes can be misused in sexual terms and the best one I've read someone quoting Ragnaros: "TOO SOON, EXECUTUS!"