There is a wealth of valuable resources on the net - it's all a matter of being able to find them. This is a categorized collection of web design resources I've found useful. Ten random entries appear below.

ColorPic
A downloadable application which works like an eyedropper tool that you can use anywhere on your screen.
OpenPhoto
OpenPhotos photos are licensed via Creative Commons. Photographers have their own sites here as subdomains. Over 2000 photos.
ColorCombos.com
Includes a combo tester to view color combos, and a color library for ideas.
SimpleBits
Dan Cederholm's design studio.
CSS Beauty
CSS Design Showcase
PHP Language Reference
Straight from the source: php.net
Graphics N Graphic Design Blog's List
Another long listing of free stock photo sites
Marek's CSS Workshop
Some good CSS tips and techniques
12 CSS Tricks / Tips
A nice compilation of links with 12 nice CSS techniques
W3C's HTML and XHTML FAQ
A good FAQ by W3C on HTML and XHTML