Flickr:

Flickr’s new service for Apple TV brings all your photos to life on the big screen, where you can engage with the Flickr community, explore the world’s most interesting photos, and use our powerful search capabilities to browse billions of photos within the most extraordinary online photo collection.

For the first time with Apple TV, sign into Flickr and view all your photos, videos, Favorites, Albums, and Groups. In one click, make any album into a slideshow or screensaver ready to share with friends, or customize in real-time with over fifteen different slideshow and screensaver modes.

I haven’t had a chance to try this out but if it works as advertised, I will use this a lot.