First:
http://www.mashuptown.com/
Was just sent this link this morning, currently enjoying DJ John's Victim of da Funk (Eagles vs. Daft Punk)
Second
http://www.djearworm.com/
Personal favorite from Earworm is still No One Takes Your Freedom (Scissor Sisters - Take Your Mama vs. The Beatles - For No One vs. George Michael - Freedom '90 vs. Aretha Franklin - Think)
It's musical magic.
Enjoy everyone.