Launch.com
Use the names of existing artists you already know, or would like to know, and click on Similar Artists. It helped me find tons of music, and if you fool around, eventually you'll find yourself in a whole new genre of music. And then you'll be obsessed with it.
I'm an illegal downloader. I don't download up-and-coming artists, only those who've already made a few albums and already bought a mansion.
Please don't hassle me on this. I really don't care that becuase of my actions Radiohead can't afford another jet to park in their backyard this year.