The Rdio Web Service Python SDK by Rdio access the API to make requests, with the aim to implement music streaming. It includes OAuth authentication. Rdio has been recently acquired by Pandora. For integration updates, follow @Rdio on Twitter.
The InternetDJ API opens this electronic music site to your app. Since 1997 (not a typo!) composers and fans have been able to share and mix music and videos. According to the API's website, requests are limited to 5,000 a day, responses are in JSON and an auth key is required.
Decibel launched its first API in 2011. Since the launch, Decibel has enjoyed success in becoming the fastest growing European company in the digital music sector. However, the massive growth falls short of Decibel's ultimate goal. Decibel hopes to enhance the consumer relationship with digital music and uncover the next generation in digital music services. In the end, Decibel aims "to become the industry standard for music metadata."