HTML5-Wiki is being developed as the next major revision of HTML (Hypertext Markup Language), the core markup language of the World Wide Web
HTML 5 Tag Reference at W3Schools
What is the WHATWG?
The Web Hypertext Application Technology Working Group (WHATWG) is a growing community of people interested in evolving the Web. It focuses primarily on the development of HTML and APIs needed for Web applications
Current HTML HTML-4
HTMLHelp.com is maintained by the Web Design Group to provide Web authoring reference material, tips, and answers to frequently asked questions