Video visualizations of how the HTML rendering engine underneath Firefox's hood renders mozilla.org, a Wikipedia page, and Google Japan.
Quick quiz: how many HTML tags can you name in 5 minutes? I found this to be pretty difficult out of the context of actually needed to code something. That and I'm kinda rusty with any non-<blockquote>/<a> HTML.
WindMaker adds motion to a web site based on the current wind conditions at a place of your choosing. Here's kottke.org with NYC wind and with Chicago wind. (thx, jim)
David Galbraith notes that several of the top sites on the web don't validate: Yahoo, Ebay, Amazon, Google, and even "Web 2.0" newcomers Flickr, Digg, and Del.icio.us. "Are all these companies wrong, or is there something wrong with current accessibility standards?"

