Writing for the Web
HTML
Simple List of Basic HTML codes
NCSA's Beginner's Guide to HTML
Janice Walker's HTML Authoring for Beginners
Color Guides
Bruce's Guide to Web-Safe Colors (216 colors identical across platforms)
Joe Burns' Color Codes
(colors which browsers recognize by name)
Graphics Collections
Web Museum Index (source for museum art)
Julianne's Background Textures (if, against all advice, you have to have a background, these textured tiles are less noisy than most)
Design
Web Page Design for Designers (Joe Gillespie)