For those that are unfamiliar with the "mash-up" premise, it is simply taking 2 or more songs and mixing then together. By mixing them together I mean that, for example, the lyrics to one song can be played over the top of the instrumental to another song, as opposed to one song leading into another (club style).
Today's example of fine work is a mix between Snow Patrol's "Chasing Cars" and the classic "Every Breathe You Take" by The Police, brilliantly called "Every Car You Chase" by Party Ben.
Snow Patrol vs. The Police - Every Car You Chase