Recommended Materials
Bulletproof Ajax by Jeremy Keith. Great concepts dealing with browser compatibility, graceful degradation, and accessibility.
Transcending CSS by Andy Clark. A design-oriented development book filled with influential code.
Bulletproof Web Design by Dan Cederholm contains guidelines to help prepare for worst-case scenarios.
the Zen of CSS design by Dave Shea and Molly E. Holzschlag. Based on the CSS Zen Garden.
Thinking With Type by Ellen Lupton. An overview on type, text, and layout. Great for beginners with type.