http://blog.greweb.fr/2012/05/illuminated-js-2d-lights-and-shadows-rendering-engine-for-html5-applications/
Illuminated.js is an open source library that let's play with light and shadow on your pages. Try the interactive demo.

A stunning 4K (yes 4K) demoscene that' recently become popular.

http://webglsamples.googlecode.com/hg/caves/caves.html
This demo lets you move through a simple landscape and punch through the terrain to create structures like caves and natural bridges.
