I think Allmusic.com lists formal connections.. although not graphically..

Yeah, of course it does, but the other problem is that you only see one level of relation. There's the artist or group, and a list of all the formal relations to that artist or members of the group. That's not the "family tree" type thing I'm looking for.

Besides, if I'm looking for new music (of the variety I already like), that's actually the way I've always gotten into new bands. I get into a band, and if I like them I find out what else its members have done, or sometimes what's more interesting is finding out what they listen to.