I've found a few sites that experiment with remixing. They include stories with a creative commons licence so you can play all you like.
And to turn to music, the medium that has been remixing for the longest: here is DJ Shadow's Midnight in a Perfect World and a remix of Midnight in a Perfect world from Endroducing. (DJ Shadow's album Endroducing is composed of entirely appropriated remixed and reworked samples and was the first ever album to do so).
First is the original piece of music that DJ Shadow sampled from:
and here is Midnight in a Perfect World:
and a remix of Midnight in a Perfect World: