I love this kind of stuff, whether you refer to it as "Bootie" or a "mashup", sometimes the sum is greater than the individual parts.
Search for Best of Bootie, as well as artists like DJ Earworm or Girltalk.
Also check out http://bootiemashup.com/blog/ Do yourself a favor and download DownThemAll! for Firefox or Chrome and you can bulk download the mp3s as you're browsing the bootiemashup site.
One that blew my mind, even after the novelty of a metal/pop mashup faded was Psychosocial Baby, a Slipknot/Justin Bieber mashup. I don't know if Slipknot lyrics or Corey Taylor's commentary are SFW, so view at own risk.
Here's an interview regarding the mashup with Corey Taylor, the lead singer of Slipknot.