Rdio takes many of the changes we've seen in music sharing over recent years and compiles them into a single, easy-to-use interface that offers a bit of everything for different types of music lovers.
Rdio's function is straightforward. Subscribe and gain instant access to 20 million songs. Create playlists, download other playlists, or search for bands or albums you want to listen to. Where it stands out is the deep social integration and the ability to create and download playlists to your device for offline listening--something other services like Pandora don't allow. The interface is very intuitive, focused almost exclusively on the music, but with numerous features including recent activity tracking, new release lists, pre-made playlists and a queue of your current playlist. You can also share with other users or follow them to discover new tracks faster.
Because of the freedom Rdio gives you over how you play your music (and where), there is a cost. Basic service starts at $15/month and is done through in-app purchases. The app doesn't do a lot if you don't have a paid account, though you can try it for 14 days the first time you download. While Rdio isn't perfect, it is one of the better music subscription services on the App Store and well worth checking out for anyone constantly looking for new tracks.