BrainJar.com features technical articles, tutorials and examples of programming for the web. It's not intended as a "cut and paste" site but rather a learning resource.

At W3Schools you will find all the Web-building tutorials you need,
from basic HTML and XHTML to advanced XML, XSL, Multimedia and WAP.

Drag-and-drop Sortable Lists in javascript and CSS

Index of all CSS selectors, their values and, most important, their support by respective browsers

Page listing various css filters for validating the various browsers