Probably the most clever name for a website...

http://twoyoutubevideosandamotherfuckingcrossfader.com/

"Two YouTube Videos and a Motherf***ing Cross-fader"

Click here to go...it's what it sounds like...two youtube videos side by side that you mix together with a motherf***ing cross-fader. Searching YouTube is enabled so you can pick pretty much any two videos you want to mix together.

Enjoy.