HTML 5 is the next major revision of the core markup language of the World Wide Web, HTML (hypertext markup language). Its first draft appeared on January 22, 2008.
HTML 5 specifies two variants of the same language, a “classic” HTML (text/html) variant known as HTML5 and an XHTML variant known as XHTML5. This is the first time that HTML and XHTML have been developed in parallel. HTML 5 is said to become a game-changer in Web application development, one that might even make obsolete such plug-in-based rich Internet application (RIA) technologies as Adobe Flash, Microsoft Silverlight, and Sun JavaFX. – wikipedia
I was just starting to explore HTML5 and try to dig it deeply as I could. And the way I learn things is going backward, so I started my exploration by finding working sites using HTML 5 markup and hit Ctrl+u in my keyboard and explore the code. I listed here the sites that i can found hoping that it could also be useful for you as well.
I know its quite a short list. But it helps me a lot in learning HTML 5.