The Music app now features an interface similar to the iTunes Store on OS X with scrollable panes and category menus. You can preview songs, browse artists, and make purchases of tracks or albums.
Notably, selecting an album will automatically highlight the most popular single for that title. Purchases can be played on the Apple TV or downloaded to another device.
Apple also has free 'Singles of the Week' available for download.
It's unclear when Apple intends to release this functionality; however, it will likely be available at the same time or earlier than the release of iOS 7. Check out a few screenshots below...