I was very excited to see the American Reunion movie. I saw American Pie just after college and remembered it was quite funny.
Jim, Michelle, Oz, Heather, Stifler reunite for their high school...
He did a bunch of these at one point. He basically would throw all this stuff onto a mix, then take it back off, but keep the early versions around for club remixes. I really wish he'd do an album of them.
And this falls more under the catagory of "Sound Collage", but I still dig:
Negativland - Gimme The Mermaid mostly because it's a really cheeky statement on copyright laws and fair use policies, which for any mash-up artist, are silly annoyances.
ToTom is probably my favorite mash-up artist. He tends to go above and beyond the typical "make a hip-hop beat using this riff" formula many DJ's stick to.