Spotify is the über-popular music service that lets you stream a huge library of music to your computer. You can also use the service on your iPhone with a premium subscription, letting you either sync and listen to your own music, or stream Spotify's tracks straight to your mobile device wherever you happen to be.
The service just recently opened up an API for app developers, and a new app called SpotON Radio is one of the first to take full advantage of it. Unfortunately, it requires a premium Spotify subscription to work, but if you have one of those already, SpotON will let you listen to Internet radio stations, your own Spotify playlists, or any other music Spotify offers. The app uses "music intelligence" from Echo Nest for recommendations, and as you can see above, the display is clean and clear, which is always nice.
If you already use the Spotify app on your iPhone, the choice of this one is really up to you -- that Echo Nest integration might offer some different music, and you may prefer the look and feel of this app compared to the official one. If you're interested (and you have the account to go with the app -- unless, like me, you just stick with the free Pandora service), SpotON Radio is free to download right now at launch.
Update: A previous headline on this post stated that Spotify was behind this release. That was a mistake -- the app was produced using Spotify's API, but by a third-party developer.