I have really gotten into this website lately!
http://www.live365.com/index.live
There are thousands of stations here and I've found so many great stations, and I'm still looking for more great ones.
Post some of your favorite stations here.
I haven't dug too deep, but I so far I've found American Top 50, Top 100 Hits, Creative Reaction, and Don't Stop the Music, all which air great music. American Top 50 is like the perfect pop station. Top 100 Hits is music from the iTunes Top 100, Creative Reaction plays a lot of underrated artists. Don't Stop the Music is very pop/rock oriented. A lot of classic hits played there as well.