2011-03-16, 19:55
Not sure if it's been mentioned, but I've used tagging software that utilizes the MusicBrainz database with great success. I'm not sure if they offer an API-like method of querying, but it might be worth a shot in looking to see if it's useful.
http://musicbrainz.org/
Edit: looks like they do indeed http://musicbrainz.org/doc/Developer_Resources
http://musicbrainz.org/
Edit: looks like they do indeed http://musicbrainz.org/doc/Developer_Resources