Underheard.Org aims to bring the best of independent radio to the entire Internet community. The idea is to promote radio stations and podcasts playing music that’s hard to find on conventional broadcast channels. Run voluntarily by a small group of music lovers and technologists the about page states;
"We’re here to show you what’s possible when you don’t have to grab every dime of available profit; when radio is driven by the music. When the music is chosen by by the whims of the the DeeJay, and whatever he’s been drinking that evening."
There’s an excellent collection of user supported shows providing alternative content for most contemporary musical styles.
If you’re looking for good Internet radio stations you can also try these recommendations for an alternative to corporate rock radio.