Last.fm isn't completely free and unlimited
"Last.fm reserves the right to share in revenue generated from your use of Last.fm Data in future on terms to be negotiated in good faith between Last.fm and You."
Discovered the FreeCover website API a few minutes ago searching for the same thing:
http://www.freecovers.net/api/
For the record, ROVi seems loaded (they source Apple):
http://developer.rovicorp.com/
...but same as every good service on the internet: if you want good (meaning reliable) service, you'll have to pay eventually ;)
