Every so often when you fire up the Apple TV, you'll see a new channel or two appear as if by magic. What do they show? Wonder no more, because it turns out Apple has a "What's on Apple TV."
What's on all those channels? Apple has the scoop.
Apple has a page titled What's On Apple TV to show all the different content available on the Apple TV. They have descriptions for the channels from Apple that display your own content on the TV, but they also included the current list of channels and what they have to offer.
Ooh! Red Bull TV is new!
Not only do they list the channels, but there's a "new" flag on the recent additions. Just like all the channels, you can always hide channels you don't want to see, or move them around to your liking. Another helpful thing on this page is the fine print at the bottom which includes the subscription requirements, or the eligibility restrictions (if any), with links to more info.