For once I was happy to see a 404 page. Over at GitHub 404 they have a very nice graphic informing you that the page doesn’t exist. Better still, when you hover over the graphic it has a 3D effect! Go and check it out.
The effect uses HTML5, a series of individual graphics, absolute positioning and a technique (if you know the name please add to the comments as i’d love to know) to identify your current mouse position and alter the graphic on the fly.