• Avoid "Best viewed with ..." - use HTML 3.2
• Use permanent URLs (for bookmarks) and symbolic links.
• Use server-side includes for navigation, copyright - avoid broken links.
• Check links automatically and periodically.
• Watch your color scheme.
• Sign and date.
• Avoid click here - make printed document readable.
• Write prose instead of lists - unless it's a list.
• Remember the text-only users: IMG ALT
• Test your HTML with several browsers.
• Use WIDTH and HEIGHT on image maps.
• Use frames sparingly, if at all.
• Use structural markup where possible: <em> instead of <i>.
• Use ISO characters instead of &
• Avoid use of H2, etc. for size or boldness.

Web design manual

Open-source web designs

A style guide

Glass dog, also more advanced topics such as style sheets

BlueRobot layout (panels, menus)