Spoke too soon… MusicBrainz is a collaborative open database which stores music metadata. This project allows the internet community to uniquely identify a digital piece of music and look up related information such as title, artist, album, etc. MusicBrainz allows users to look up information about CDs as well as individual MP3s/Ogg Vorbis files.
Looks like the project is a bit stalled right now, but it does have ambitious plans to become a comprehensive geneology, tracking influences and participants. Interesting. Currently supported by FreeAmp
MusicBrainz Metadata Initiative 2.0, Aaron Swartz’s article, MusicBrainz: A Semantic Web Service (PDF)
Others: MusicDB, Open Music Database (planning),