W3C - The World Wide Web Consortium (W3C) was created in October 1994 to lead the World Wide Web to its full potential by developing common protocols the adoption of web standards. This is a good site to learn more about web standards and the development of HTML.
TheWebsEye.com - covers the basics of web design including web design books and free web design resources
wpdfd.com - Web page design for designers - Joe Gillespie's excellent site about web design!
WebReference.com - an excellent site with links to other HTML resources and tools.
Web Design Group - Ab HTML site focusing on accessibility
HTMLGuru.com - The Guru site is a Dynamic HTML resource for web developers seeking to explore new horizons in web site design using the latest cross browser Dynamic HTML.
The HTML Writers Guild - provides online web design and certification.