I’ve just been playing with finetune.com. This website allows you to pick an artist and they will build you a playlist featuring music by that artist and other related artists. You can then listen to that playlist and remove songs you dont like and add others you do!
The artists include mainstream popular artists! So you can listen to pretty much any band you want. There have not been many artists I was unable to find.
Once you have made a playlist, you can share it with others. There is even a widget for your blog or myspace profile etc. And even better! They have a special page optimised for the Nintendo Wiis built in browser so you can instantly turn that into somewhat of a media center. I recently used this at a party we hosted and it worked great!