First of all I want to say that by "free", (as the famous quote goes) I mean freedom, and not as in free beer.
The following are some sites that offer music under "open" licenses. I guess they are already well known, but just to bring it to the notice of anyone who is interested, here they are :
[*] Jamendo - Jamendo calls itself "the largest royalty-free music catalog in the world". All (or most) of the music is licensed under the creative commons licenses. http://www.jamendo.com/en/faq
[*] http://www.freesound.org/ - freesound.org has a huge variety of sounds, all licensed under the creative commons licenses. http://www.freesound.org/help/faq/#freesound-0
[*]ccmixter - ccmixter's about page describes it as "a community music remixing site featuring remixes and samples licensed under Creative Commons licenses." http://ccmixter.org/about
sources/more links
http://supertuxkart.sourceforge.net/Licensing#Where_to_find_files
http://www.hongkiat.com/blog/creative-common-music-download/
Hope this helps anyone wanting to contribute by bringing to attention any music/sound/loop that can be used in this project.
Be sure to check the specific,individual, license of any music/sound/loop you may think of.