There is a piece of software out there that does this. I have a trial installation of it on my PC at home, but for the life of me I can't remember its name.

Basically, it scans your entire MP3 collection and makes a database out of it. You can pick a song and hit "more songs like this one" and it'll come up with a pretty good match of it. In the limited testing I did with the trial version, it seems to do what you're looking for.

Anyone know the name of the software I'm talking about and have a link to it on the web?