When I was a kid, I was big into stereoscopy ("magic eye"). I was bored today and thought I'd see what people had made lately. This, by far, was the coolest:
http://video.google.com/videoplay?docid=-254396095535185418It's a cross-eyed stereogram, which means you have to focus close (go cross eyed) to see it. It took me awhile because I used to always do parallel stereograms (when your eyes move apart).
To view, I suggest putting your finger against the monitor and focusing on it. Then move it toward yourself, continuing to focus on it, till you can see the image. It's really cool to poke at the image with your perfectly-in-focus finger and watch it fade in and out. Very cool stuff!