UPDATE, January 16, 2007: Links to the mash-ups featured here no longer work. Mark Vidler is set to release a mash-ups album in cooperation with EMI. Go to GoHome Productions for more details.
After hearing a fair amount of mash-ups, it's clear to me that the best ones re-introduce a song or two (or more) you may already like and then uncover other parts of their personalities, perhaps making you love them. More subtleties, other aspects of melody and structure, new emotions not present during previous listenings, are revealed.
Here are three prime examples of this from the mash-ups master Mark Vidler.
1. "Flaming Mary Can (Out) Run Prince" — An all-star mash featuring the Flaming Lips, Mary J. Blige, Can, Run DMC and Prince. Classic. Wayne Coyne speaks to us about art at the beginning.
2. "Marvin's Not in Love Parts 1 & 2" — This ballad nostalgia trip, featuring Marvin Gaye and 10CC, keeps true to its roots until about mid-way through the mix. It then breaks into an uptempo, electronica-lounge switch, bringing decades-ago hits into the 21st century.
3. "Essex Doves" — David Essex's "Rock On," mashed with the Doves' "Firesuite," sounds completely new.
Some mash-ups that I've heard don't make sense musically and aesthetically. Most of Vidler's that I've heard are so well put-together that they stand strongly on their own as new works.