I've done some of icecrown which like Zal says, is a lot of kill quests, which makes for nice exp, however i'm stuck with only collection quests left at the minute after doing the first few starter ones, so back to standing around afk without having the energy to quest... !

I found karazhan gives exp at 78 still though. 900xp a trash mob or so, in a raid with 5 people.