This is my first adventure into the world of mash-ups.  Michael Jackson vs. The Gorrilaz.
It's a simple A+B type deal, but I think it works well.

Beat It So It Feels Good, Inc.

Beastie Boys vs Queen

Here's another simple one.  I didn't have to do much at all really.  If I had any real skill with these programs I'm sure it would be better, but it's not too bad for an amateur like me. 

Intergalactic Dust Biters

Garbage vs The Supremes

I Think I'm Paranoid vs Stop! In The Name of Love

Here's another quick mash-up for your enjoyment.  This one feels pretty solid to me.

braktokus