The Spotify Web Java Library provides a wrapper to the Spotify Web API. The library provides helper functions for interacting with your music library, authentication, browsing, searching, profiles, playlists, and music metadata.
Yes.com is a unique community-oriented music site that provides real-time and historical information about songs played on United States terrestrial radio stations. Besides this up-to-the-minute database, Yes has social features like chat rooms for specific radio stations or for a specific artists, like the Yes.com Pink Floyd page showing which radio stations are currently playing or recently played Pink Floyd songs. In addition they also offer an API that developers can build on (our Yes API profile).
If you are looking for sound samples on the web and want to add them programmatically to your apps, the Freesound API may be just what you need. Freesound is a collaborative database of Creative Commons Licensed sounds. Users can join Freesound and upload their sound files and share it with others. Recently it also announced that it has crossed 100,000 songs in its database.