At A List Apart most of the articles published on the topic of CSS come in from web designers sharing their thoughts and breakthroughs with CSS-enabled design.
BlueRobot.com Layout Reservoir
http://www.bluerobot.com/web/layouts/
This small but valuable resource covers two- and three-column layouts.
CSS-Edge
http://www.meyerweb.com/eric/css/edge/
Eric A. Meyer's workshop displays some of his more advanced CSS experiments.
CSS Zen Garden
http://www.csszengarden.com/
The CSS Zen Garden showcases web developers from all over the world restyling the same content. Surfing through several designs is not only great inspiration, but also a fantastic way to better understand the concept of separating presentation from content.
Glish.com CSS Layout Techniques
http://www.glish.com/css/
One of the first collections of multicolumn layouts created in CSS without the use of HTML tables.
Microformats
http://www.microformats.org/
Defines and promotes standards for coding unique pieces of content. Check the Microformats listing for methods to code common data like calendar events, contact information, or even the abbr element.
Real World Style
http://www.realworldstyle.com/
A design resource managed by Mark Newhouse, the goal of this site is to promote CSS-enabled designs, not only for modern, popular browsers that run on Macintosh and Windows OS, but also for browsers that run on Unix machines.
SimpleQuizes
http://www.simplebits.com/bits/simplequiz/
Web designer and author, Dan Cederholm, conducted a series of quizzes trying to determine the best methods for marking and styling common web development scenarios. In addition to reading the conclusion to each quiz, read each quiz's comments by web designers to get a more informed opinion on coding practices.
Typetester
http://typetester.maratz.com/
A flexible tool that allows web developers to customize three sets of type and then generates the basic CSS for easy copying and pasting. Available features include setting the values for fonts, size, tracking, leading, letter spacing, alignments, and more.