Mashup (mash-up) "One song to the tune of another", A combination of two songs.
Finding 5 mashups that were 1. any good, and 2. contained two songs that I actually knew (and at least one I kinda liked), was a bit of a challenge really, but here are my 5 Top Mashups....
Nirvana Vs Rick Astley
Queen Vs Outkast
Britney Spears Vs Gwen Stefani (Yes it's Britney. I'm sorry. Really, really sorry...but it does work so it's worth a listen)
Snow Patrol Vs The Police
Korn Vs Coldplay