Vevo had been rumored to be preparing an app for the Apple TV for quite some time. Their app lets you select music videos to listen to on-demand or you can also watch the Vevo TV channel. More details here.
Disney's apps are accessible to viewers with a pay TV subscription from one of the major providers. The apps provide access to a live feed with on-demand options.
The Smithsonian Channel app offers on-demand clips as does the Weather Channel app; however, in certain cases (ie. large storms) the Weather Channel will provide a live feed of the pay channel.
You can get the update by selecting Software Update from the General menu inside the Settings app.
[Additional images via 9to5Mac]