I would like to suggest adding access to the Freesound archive (<a href="http://www.freesound.org" rel="nofollow">www.freesound.org</a>). They have a TON of sound effects (which is where I personally find SoundCloud lacking) and lots of ambient tracks as well. All sounds are released under creative commons.
I looked into it and they offer an API (<a href="http://www.freesound.org/docs/api/" rel="nofollow">http://www.freesound.org/docs/api/</a>) which looks pretty easy (depending on your implementation of the jukebox, of course :).
This seems like a feature that would add a LOT of value to the Roll20 community.