HTML5 is certainly the technology of the future and a lot of fun to play with. I’m going to go ahead and play with it on this page. This will also be a great place to list resources.
What better place to start than the World Wide Web Consortium (W3C). The specification is at https://www.w3.org/TR/html5/ and, while it’s rather dense it is definitive. If you want to ensure you are compliant this is the place to go.
Of course, you will want to test your site and what better place, once again, than W3C. Going to https://validator.w3.org/ and entering any site address will give you and excellent overview of any problems you may be having. Some of the errors are invalid but the site can give good insight into the general health of your site.
I love Wikipedia for technical information and the HTML5 page does not disappoint. The excellent W3CSchools has a fantastic tutorial / reference page. Another resource is CanIUse for browser support and compatibility issues.