Sites that Help Web Designers

A List Apart
This is a great resource for anyone who builds web sites. Their focus on standards and best practices is very practical and they lead the popularization of many great methods (like Suckerfish Drop Downs).
Listmatic
This site was invaluable when it came to getting the navigation for this site functional and correctly aligned across browsers. IE is picky about LIs, and even worse about horizontal ones. Listmatic is the best resource on lists I've found.
IE: On Having Layout
This article explains SO MUCH about the idiosyncrasies of Internet Explorer that had previously eluded me. It's a must-read for anyone experiencing difficulty with layout in explorer.
Position Is Everything
Clearly a programmer's (as opposed to a designer's) website, this is a powerful resource that describes bugs and corresponding fixes for various browsers (mostly IE). My only beef is that they tend to suggest in-line hacks, rather than conditional style sheets. The concepts are sound, however, and the results are as advertised.
Bruce Lawson: Conditional Comments
This describes the clean way to accomodate various browsers—conditional comments. This allows various browsers to be target specifically, and avoids issues like those which arose when IE7 came out, which responded to the same hacks but acted more in line with CSS standards.