Apple on Wednesday announced the additions of HBO Go and WatchESPN to the Apple TV. Those are channels that the Roku has long offered, but they're new to Apple's set-top box. Despite reports that it was coming soon, the CW still isn't on Apple TV.
HBO Go allows subscribers to stream all of HBO's programming on demand, including all of its older shows like The Wire and The Sopranos, along with all of the movies currently showing on HBO. Not all HBO subscriptions include HBO Go access; it's up to your cable company to support the service. DirecTV is perhaps the most prominent provider not to support the Apple TV for either HBO Go or WatchESPN, though it does offer access to the HBO Go app on iOS, which can then--somewhat convolutedly--be watched via AirPlay on the Apple TV.
WatchESPN simulcasts ESPN, ESPN2, ESPNU, ESPN Goal Line, and ESPN Buzzer Beater, though again, access is at the whim of your cable provider. ESPN3 exists solely on WatchESPN.
In announcing the arrival of HBO Go and WatchESPN, Apple also said that iTunes customers have downloaded more than 1 billion TV episodes and 380 million movies, and that they purchase over 800,000 TV episodes and over 350,000 movies per day.
The other new providers on the Apple TV as of Wednesday are Sky News, Crunchyroll, and Qello, which live news, anime/manga, and music programming, respectively. Access to those providers, like all the others, depends on both your geographic location and your cable provider.
You'll need to update your Apple TV to the latest software to gain the new channels.
Updated at 8:24 a.m. PT to note unavailability for DirecTV customers.