John Moriarty's CSS Resources on the World Wide Web
Basic Layout and HTML > CSS Info
hTMLDOG.com/ A great site: clear, succinct explanations of HTML and CSS, and what each is for. Look for the HTML Dog book - one of the two best I have seen - with the best discussion of Layout (HTML) vs. Design (CSS).
A List Apart - Topics This is the preeminent site on CSS. Some of the material is a bit dated.
hTMLDOG.com/ Whether you are a beginner or advanced user: A great site: clear, succinct explanations of HTML and CSS, and what each is for. Look for the HTML Dog book - one of the two best I have seen - with the best discussion of Layout (HTML) vs. Design (CSS).
FluidDesign More (or maybe the same) fluid design info.
A List Apart - negative margins One of the most influential and informative sites, although some of the information is dated, now. This is a particularly interesting article about a very NOT intuitive use of negative margins to position floaters.