my favorite is m1live.com, which plays the currently popular dance/trance and house tracks, no unknown/boring stuff like DI (sometimes), and no real cheesy stuff either
if you're into the Belgian-Euro flavor of trance, then check out c-dance.be
c895fm.com is a local Seattle radio station, mostly dance music and mass-appeal stuff
a good site for stream links of all music genres and countries is mikesradioworld.com