One of the most awesome mash-ups out right now is a mix of Rick Astley's 'Never Gonna Give Your' and Nirvana's 'Smells Like Teen Spirit'. This takes Rick-rolling to a whole new level.
It has recently become fashionable for Classic Rock artist to do Mash-up versions of some of the most beloved Classic Rock songs ever recorded, with a big Rap or Hip-Hop tune.