Your Ears Need This: Tainted Jesus (Soft Cell vs. Depeche Mode)
There's a lot of crappy mashups out there. Sometimetimes it's just some idiot playing two songs at once. Sometimes it's mixing two songs that are already so similar that you aren't sure if it's the original or not.
But when mashups are good, they're spectacular.
For example, DJ Lobsterdust's mashup of "Tainted Love" and "Personal Jesus". It works so perfectly, capturing the essence of both originals while still creating something completely new. Give it a listen and look below (excellent mixing with the video), and you can grab the mp3 at Lobsterdust's website.