Free-loops much like Freesound is a collaborative database of audio snippets, samples and loops openly licensed for use. There is a wide array of audio available but most of the categories are built around instrumentation, so this could be a great resources for electronic musicians and audio programmers.
Freesound has less audio in full song format and more in the way of audio snippets, samples, recordings, bleeps and loops openly licensed for use. This is actually where I ended up finding the audio I needed for my project. There is a wide variety of audio available here from samples of nature and industry, to audio jingles and riffs.
ccMixter is a community remix site sponsored by ArtisTech Media and created by Creative Commons. ccMixter offers a bit of everything including remixes, podcasts, samples and a-cappellas which can be used for remixing or in mixed media projects.
Like the Free Music Archive, Jamendo allows users to download and listen to songs and albums from up and coming artists. Even further, Jamendo has a series of radio channels available by genre which allows listeners to discover and share new artists.
The Free Music Archive is described as an archive of public domain and Creative Commons licensed songs managed with a curatorial approach. The bulk of the audio available here is in the form of full songs from artists around the world. The Free Music Archive gives up and coming artists a place to share their bio and link to their home page so that users can learn more about the music they discover.