The Wub Machine - Turn any music into Dubstep, Drum & Bass, and more.
The Eternal Jukebox - For when your favorite song just isn't long enough
Madeon's Adventure Machine - Online remixing tool
YOU.DJ - Mix SoundCloud music and Youtube videos live in your browser.
Remixatron - Infinite Jukebox on the command line in Python.
The Infinite Jukebox (at playlistmachinery.com) - Re-hosting of the now-defunct Infinite Jukebox.