CSS

Cascading Style Sheets. Check out the CSS Zen Garden and meyerweb for classic examples.

• Pure - a minimalist CSS toolkit.
• unsemantic - a percentage-based grid system.
• InK - SAPO's CSS framework.
• Blueprint - a CSS framework with sensible printing defaults and grid layout support
• CSS redundancy checker - requires Ruby, but seems pretty useful.
• cssutils - a Python library for parsing and manipulating CSS.
• Techniques, by category.
• Dynamic Drive CSS Library
• The CSS Playground - lots of fun to be had.
• PVII Dreamweaver extensions lots of DHTML and CSS pre-built extensions for Dreamweaver
• Drop Shadows
• Slants (heck, every CSS geek has a link to this, even if it's fiddly to use...)
• Lists and DHTML menus
• Tables

If you're looking for the CSS DVD algorithm, the DeCSS Gallery has several renditions of it (and full coverage of the folly that ensued when it was broken).