Sad Steve is a single-purpose search engine with a fairly familiar mascot. It is completely devoid of advertising, and it makes no money at the moment (according to the informatively-titled What? page).
It’s run by a guy named Joe Huttner, and it does just what it says on the tin. You feed it with the name of a band or a song that you like and it comes up with an MP3 of said song (usually, a bunch of MP3s). Then, you can listen to the song or download it.
Sad Steve also features some indie-looking bands, and it even has profile pages for them (check out Halo Stereo). It’s no Muxtape or Bandcamp, but for some bands I suppose the format works. If you have an account on Sad Steve, you can pledge money for bands that are listed on the site (I suspect that “pledging” is probably not the same as actually paying, but I’m not sure).
All in all, I’ve seen more polished efforts in the online music/search/indie band page space, but Sad Steve combined all three functions and it’s been around for a while. It’s certainly handy as an occasional search engine, but if you don’t have a problem with Flash, I would go for an app like Grooveshark.