I was surprised Simulchart did not make TCs short list. It's superbly executed, a perfectly functional beta product (I've been told by the developers themselves that they plan on taking it over the finish line in the coming weeks), has a dead simple API, works across all browsers, and is immediately marketable. Not to mention, it's just plain cool.
http://awesometown.no.de/
http://www.viddler.com/explore/matschaffer/videos/1/simulcha...