Here in Portland there's a station called 94.7 KNRK--"Alternative Portland," which in my opinion is kind of a redundancy; Portland is pretty damn "alternative" on its own--and on Saturday nights you can catch Squid's Modern Mix, which features mashups of modern songs with classics.
This is how I discovered such amazing things as:
Jimi Hendrix vs. Muse: "The Blackout Cries Mary"
The Rolling Stones vs. the Dandy Warhols: "Sympathy for the Warhols"
Both of which are FUCKING AMAZING.