Some Music Links

Discogs - Huge discography database
Dogmazic - lots of Creative Commons music (mainly French)
Whitburn project - 120 years of chart history
Artists facts and Song facts - lots of facts about songs and artists
Classical.com - Huge database of classical music
Grove music encyclopedy - *The* ultimate resource for all sorts of information about western music
John Peel Festive Fifties - Actual content of John Peel sessions (would be cool to link to that from the BBC John Peel dataset)
Musical knowledge webs - Some general music information, appears to be quite structured
Bach cantatas - All Bach Cantatas
Concert Programmes - Large concert database (performers, venue, works, etc.)
Laytune - Audio web search by artist/track/album
Songkick - Huge database and recommendation service for live music
OLPC sound samples - Big database of Creative Commons audio samples
FreeSound - Huge database of freely available audio samples
OperaGlass - Huge database of Opera - 25,000 operas, 4,800 composers
Wikifonia - Repository of lead sheets
JSBach - Complete database of JS Bach's works, by BWV number
Mozart forum - Listing of Mozart's works at MozartForum following the listings in the 6th Edition of the Köchel Catalogue
Librivox - Freely available audio books
Music digital repositories - Huge list of music digital repositories
Musicbrainz listings of musical works per composer