The World Wide Web Consortium has been in existence since 1994, and its purpose is to set standards for the web. For any standards-related question, this is the place to go. This is also the place to get your HTML and CSS validated.
On-line tutorials with try-it-yourself examples and quiz tests. Topics include: HTML, XHTML, CSS, XML, XSL, DTD, DOM and WAP.
Portal leading to a large number of excellent resources
One of my favourite web development forums, covering all aspects of web development.
Another favourite forum, with a very friendly atmosphere. Some of the forums are members-only.
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