20thingsilearned.com. A fancily designed website, that is a kinda educational article for the general public that teaches them what is the web and web technologies, together with some opinions mixed in. A sorta propaganda, from Google. However, it demonstrates what html5 can do.
The site seems to be created sometimes this month (2010-11) (or, opened to public), and it's just about 20 pages of content, but the site's already ranked 21k in the world. (See: alexa.com.) For context, my site xahlee.org is ranked world's 68k, and has about 8k daily visitors. A quick estimate seems to indicate the site gets 286k visitors per day.
See also: HTML6, Your HTML/XML Simplified.