Specifications
Behavioral Extensions to CSS, CSS ICC Profile Support Proposal, CSS Namespace Enhancements (Proposal), CSS1 Specification, CSS2 Specification, CSS3 module: W3C Selectors, Introduction to CSS3, Multi-column layout in CSS, Paged Media Properties for CSS3, User Interface for CSS3
CSS Home Page
World Wide Web Consortium's CSS Page that includes links to standards and other reference pages. Also includes news on CSS happenings.
css Zen Garden Resources Pages
A list of links to help with techniques, bug fixes, css projects and playgrounds, and tools.
DevGuru CSS2 Introduction
CSS quick reference that describes the stylesheet properties.
Dezwozhere.com
Collection of links to tutorials, layout resources, accessibility guidelines, discussion lists and editing tools.
HTML Goodies CSS Reference
Properties reference divided into categories. Also explains usage and includes examples.
HTMLHelp CSS Properties
Description of CSS1 properties split into categories and sub-categories.
Index Dot Css
Properties index, examples, and browser compatibility information. Also includes history and links.
Network Communication Design Style Sheet Guide
Property reference, including explanations, sample code, and browser compatibility information.
WebEnalysis CSS properties chart
CSS Chart displaying the cascading style sheet attributes and properties with possible values.
WebReview: CSS1 Overview
List of CSS1 properties with code examples for each. Registration required to view.
zvon.org: CSS1 Reference
Downloadable CSS1 reference with examples.
zvon.org: CSS2 Reference
CSS2 reference with examples (including aural ones).