It's Frank Black vs. Kelly Clarkson. And I'm surprised how awesome it sounds.
"Get Your Bootleg ON" is the name of the site, and it has some interesting mash-ups; unfortunately the variety of music is limited i.e. too many hip-hop mixes. But these two songs are good. And if you can find it, get DJ Assault's "Ass and Titties" vs. the Theme from Tetris, entitled "Ass and Tetris", lol.