Not really sure how I never noticed this (and it’s probably old news for quite a lot of you) but Mountain Lion supports outputting audio to AirPlay devices. I don’t use AirPlay often, but when I do it’s usually from my iPhone or iPad and will have video accompanying it.
It does make apps such as AirFoil redundant for users with a single AirPlay device (though AirFoil supports outputting to more than one simultaneously, like iTunes).
You can find the settings under System Preferences > Sound > Output
(Thanks to @fneb who mentioned this briefly a few weeks ago but it never registered).