HTML5 is the latest standard for all HTML websites. It's been in development since 2004 and is just now being added to browsers.
The spec is stil a work in progress, view it on the W3C website.
HTML 5 introduces a whole set of new elements that make it much easier to structure pages. For a complete overview and introduction to what HTML5 can offer to designers and coders, I recommend taking a look at this article over at A List Apart.
We've been running a few 101 Best sites over the last few years, take a look at some of the others:
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