Illuminated.js is an open source library that let's play with light and shadow on your pages. Try the interactive demo.
Hartverdrahtet - Akronyme Analogiker | 4k Revision 2012
A stunning 4K (yes 4K) demoscene that' recently become popular.
WebGl Caves Demo
This demo lets you move through a simple landscape and punch through the terrain to create structures like caves and natural bridges.