Yet another free, customizable radio app, but one that has a spectacularly huge music library, and that gives you fine control over the songs you hear.
Slacker is pitted directly against Pandora, and they do a lot of similar things. Enter an artist or term to create a new radio station, though, and they'll give you totally different, but equally awesome, streams of music. And hey, they're free, so why not use both?
From The App Developers:
Listen to unlimited free music on your iPhone. The free Slacker Radio App gives you access to the entire Slacker music library featuring millions of songs from thousands of artists. Listen to over 100 expert programmed radio stations or create your own custom stations directly on the iPhone. Slacker Radio is the best way to discover new artists and hear your favorite songs.