XHTML and CSS Learning resources
Apple’s Web Page Development: Best Practices is a very good introduction to creating standards-conforming websites. The article brings up some of the common problems people run into when they start learning CSS layout as well as some very common XHTML coding mistakes.
The HTML Tag Reference at HTML Dog is an impressive listing of all tags allowed in strict XHTML. Each tag, along with its possible attributes, is explained in a way that makes this reference easier to read and understand than the official W3C documentation.