What's a good site that you can listen to rap music online?

Rap/hip-hop

A great site for music is Pandora Internet Radio

You can enter artists you like, and it recommends music with similar musical style. They're the same people that did the Music Genome project a while back, and they're using their research for this.

If you don't like a song it recommends, you can tell it so and it will avoid songs with those musical qualities in future.

Best of all, all the music is streaming.