Over the past decade, "Mash-Up" became a common term in pop culture. However, it's almost always been associated with the combining of two vastly different songs to make one interesting piece of music. Here's a "Mash-Up" you don't and won't see everyday. I don't even know how to accurately describe it, but it's incredible.
http://www.youtube.com/watch?v=C9jghLeYufQ