I enjoy playing around with sound and images (at a very basic level), and am often blown away by the ingenuity of mash-ups in particular. There's a lot of talent in this area, and here are a couple of my recent favourites. In the first, Chris Rule (with assistance from Nick Eckert) have recut the Mary Poppins trailer so that it's transformed into the horror genre - Scary Mary.
In the second, Frans Peter Bull Enger, aka Norwegian Recycling (visit his site for a variety of excellent mash-ups) has mashed Harry Potter into Dark and Difficult Times. Enjoy.