IODA is an online music distribution service for independent artists. IODA has a large database of artists, albums, and songs available through their website and retail partners. The data is also available through the IODA RESTful API. Users and developers can create their own applications around the information in IODA's extensive database. The API is currently still in Beta, and is subject to change.
The Independent Online Distribution Alliance (IODA) has just announced its IODA Open API, currently in beta. The API offers many of the typical resources that you would expect from a music metadata service, with a few extra goodies like these album attributes: UPC code and primary label. Comparing album API results between IODA Open and iTunes, IODA is packing a lot more information into the response.