HTML, XHTML & CSS How-To's
W3C
"The World Wide Web Consortium (W3C) develops interoperable technologies (specifications, guidelines, software, and tools) to lead the Web to its full potential. W3C is a forum for information, commerce, communication, and collective understanding."
Sizzling HTML Jalfrezi
"Sizzling HTML Jalfrezi is a comprehensive guide to writing web sites. Whether you're a beginner or a design professional, you'll find what you need here; quickly and clearly. Our unique system of examples makes Jalfrezi both the perfect learning tool and superlative web authoring reference. "
Design
A List Apart
"A List Apart explores the design, development, and meaning of web content, with a special focus on web standards and best practices."
Open Source Web Design
"Open Source Web Design is a collection of web designs submitted by the community that anyone can download free of charge!" I include this page not so you can simply download a design and use it, but so you can view the many possibilities and see the code used to create them so you can apply it to your own work.
Boxes and Arrows
"Boxes and Arrows is devoted to the practice, innovation, and discussion of design; including graphic design, interaction design, information architecture and the design of business."
CSS
css Zen Garden
"A demonstration of what can be accomplished visually through CSS-based design."
Position is Everything
Big John and Holly Bergevin "built this site to explain some obtuse CSS bugs in modern browsers, provide demo examples of interesting CSS behaviors, and show how to 'make it work' without using tables for layout purposes."
GRC's Script-Free Pure-CSS Menuing System
An outstanding cascading menu system built with 100% CSS (no JavaScript, no ActiveX, no preservatives) by John Gibson of GRC. The site also includes links to several other CSS-based menu implementations and tutorials.
CSS for the Unglued
A quick-and-dirty CSS resource with many links to other sites full of helpful information.
Details on CSS changes for IE7
Detailed listing of a number of CSS-related bugs that have been fixed in the most recent release of Microsoft's Internet Explorer (version 7). This page is also a nice listing of known bugs that may be haunting your design in Internet Explorer 6.
Accessibility
accessify.com
"Tools, wizards, articles and tutorials on Web Accessibility for the conscientious web developer."
Building Accessible Web Sites
An entire online book about the why's and how's of building accessible sites.
Browser Archives
evolt.org - Browser Archive
A repository of older versions of many of the most (and least) popular web browsers ever released. Essential for web developers looking to test their sites in the broadest possible manner.
Browser Statistics
W3C browser statistics
What is the trend in browser usage, operating systems and screen resolution? This page can tell you all that and more.