View Source Tutorial
Brad Neuberg: View Source Tutorial: Fancy Web Page Using HTML5, CSS, and SVG [via Tim Strehle]
Not only is it a thing of beauty (both visually and from a view source perspective), it also nearly validates... and furthermore the validation errors are useful. This is hopefully an indicator of the way the web is heading.
With a little content negotiation and with this bug fixed, perhaps it could even work on IE.