MusicBrainz is a service for matching ID3 tag information with acoustic fingerprints. MusicBrainz provides a C Library that can be used with cocoa. The opensource iTunes Tagger known as IEatBrainz uses the MusicBrainz library with QuickTime.
I wrote some code which computes the discid from the .TOC.plist file for MusicBrainz…see DiscID.