I may be slow on the uptake here, but Mr.doob has some awesome HTML5 and Flash Player showcase pieces over at [mrdoob.com](http://mrdoob.com/ "Open "mrdoob.com" in a new window."). It's hard to pick a favorite, because they're all darn impressive, but I'm a fan of the [Face-tracking and 3D Scene demo](http://mrdoob.com/90/Facetracking+3DScene "Open "mrdoob.com"s Face tracking and 3D Scene demo in a new window.") (which I've screenshotted above). It's based in Flash, because it has to access the computers' webcam, and is a pretty neat concept.
If it didn't require the whole webcam-access notification message that makes the whole effect so obvious, I'd definitely want to slide this into loads of projects, just for the hell of it!