The Rdio Web Service Ruby SDK by Rdio allows API interaction to implement audio and music streaming. Examples show how to authorize user credentials and create playlists from artists. Rdio has been recently acquired by Pandora. For integration updates, follow @Rdio on Twitter.
Spotify has just added the Spotify Web API to Mashape, a popular marketplace where cloud APIs can be distributed, monetized, managed and consumed. Developers can use the Spotify API to search and display data such as albums, artists and music tracks from Spotify's vast music database.