There are others out there (even i-Tunes has a "radio" tab) but these are a couple of the biggest and best known. Most of the streams are in MPEG format which plays well in Winamp, Real Player, Windows Media Player, i-Tunes, etc.
You can sort their listings by speed, genre, location, popularity. etc, and probably find a few that you like. There are both internet-only steramers there, as well as stream copies of many on-air radio stations.
Another idea might be Pandora, but if you can't get Spotify, that may be blocked too.