SoundCloud's remix contest.

from Soundcloud: "To celebrate the great collection of Creative Commons tracks on SoundCloud, we're holding a remix contest... CC style! So in the spirit of "some rights reserved", upload your best CC samples and loops and then get remixing them into brand new pieces."

CC Mashup Contest

Link: https://blog.soundcloud.com/2010/09/21/creative-commons-mashup-contest/