Listen to DI radio, like now, go scoot off and listen to it.

Ok fine, it's a "techno" site with many many many different channels of radio that play 24/7, my favourites being Trance, vocal trance, and Chillout channels (veeeeeery relaxing with a stick of insence going). Thursdays my favourite guy Armin van Buuren does a show called A State of Trance (lovingly referred to as ASoT) which is most often mind blowingly good.

I usually listen to Hardcore, Metal (core), etc. so I guess that speaks for the quality of the stations a bit. Listen on winamp for the best free quality (96 khz) stations, plus winamp's pretty cool in and of itself.