Good resource for doing web design

Checky: Mozilla-based Validator - The Checky plug-in for the Mozilla browser is an simple interface for web content and resource developers to free and commercial online validaton and analysis services, including accessibility validation, a color-blind simulator, and other services that check your HTML, CSS, RDF, RSS, XML, etc.
Another Mozilla add-on that is useful for developers is the XUL Preferences Toolbarmentioned in an earlier post about developing XUL applications. [Ed Tech Dev]