Internet Radio Epitonic
Writing about web page http://epitonic.com/radio.jsp
There are probably lots of these types of thing around, but I haven't tried any before.
Just select from some [superbly well-named] categories and up to 500 tracks appear in your Winamp playlist and um.. play.
Some utter crap, of course – but the odd gem. Lounge, Noise and Experimental are particularly special.