The most surprising dollar I've ever spent in the App Store? TuneIn Radio. There's a good deal of meat to the app, with over 50,000 stations to choose from, and the ability to preset times to record morning shows, wake up to the radio, or add stations to a list of favorites. Stations unavailable in the existing database can be added simply by typing in the URL. Available across all the platforms and via webpage.
iOS - $1 / Android - $1 / Windows Phone 7 - Free
Slacker Radio is offered at several levels: the first rung offers 150 free custom music, news, and sports stations. The Slacker Radio Plus subscription ($4/month) takes away all the ads and allows unlimited song skips, station caching, lyrics and ESPN radio. Finally, the Slacker Radio Premium subscriber ($10/month) grants access to songs/albums on demand, single artist stations, playlist creation and playlist and album caching.
iOS - Free / Android - Free /Windows Phone 7 - Free
AOLs SHOUTcast Radio directory boasts over 50,000 stations, ranging from professional to independent radio. Those who demand quality sound will love the high bitrate stream option for clarity that rivals mp3s played straight from the hard drive. I love how the interface maintains the Winamp spirit it originates from. Free
Digitally Imported Radio
Electronic music addicts will have a soft spot for Digitally Imported Radio, which specializes specifically on the various flavors from trance to house. Veterans of the electronic tunes and newcomers alike will find an easy to navigate interface. With over 37 sub-genres offered, DIR is a recommended listening destination to the 808 state. Free
Also available on Android - Free
Everything that SHOUTcast Radio for iOS has, Winamp Pro offers also...and then some. What sets it apart is the music player functions, which borrows heavily from the desktop application, making this one of our favorite Android music services. Winamp helps formulate personalized stations to suit your needs so you can hear what you like, while also serving up new content for musical discovery. $5
I personally believe the best place for listening to music is in the car. It's a enclosed space for optimal focus...and you're already there, so why not enjoy musical accompaniment during your drive? Xiia Live is optimized for the very purpose of enjoying music while on the road, with easy to navigable controls for station selection. One other helpful feature is the ability to tag a song "to buy" at a later time (or listen later). Over 40k channels are offered, with the option to play directly from a URL, and also numerous sound notifications to indicate when the app is connecting, buffering, or when the signal drops. $5
Windows Phone 7
Although Radio Hub lacks visual variety, it more than makes up with a global selection of internet stations from across the world. The app also incorporates Facebook or Twitter sharing options. The search algorithm helps users find specific bands, genres, songs, or even music specific to a country for those feeling homesick. One special touch I like Radio Hub offers is the multitasking feature, which lets listeners play the radio while using other apps so the music never stops no matter wherever you go. Free
Keeping things local and simple, iHeart Radio is built with a selection of over 750 American radio stations and channels. Windows Phone users can set the app as a live tile specific to a favorited station, making it easily accessible and quick to start up. Free
Also available on Android - Free
(Image: Gregory Han; as linked above)