While Google Sets is a robot's best shot at this, Gnod's Gnoosic really does help you find new artists you didn't know ...

Gnod is kind of a search engine for music you don't know about. It will ask you what music you like and then think about what you might like too. When I set gnod online its database was completely empty. Now it contains thousands of bands and quite some knowledge about who likes what.

Does it work? The difference between this and Google is that Gnod leverages human expertise --- I gave it several subsets of my fairly ecclectic, obscure and outside tastes, and while I was given a whack of interestingly false positives, within a few minutes I'd discovered Jimmie Spheeris and Joseph Spence ... true, it's not exactly indie material, but Gnod got a lot farther than I'd expected, and presumably the artists I'd used to find these two are now also potential recommendations for the Spheeris/Spence fans.