Here are some excellent CSS links to keep around:

• The "authority" on CSS, with links to tutorials, tools, and the latest information on Cascading Style Sheets: W3C's CSS Home Page
• Learn CSS, see samples, and even quiz yourself at The CSS Tutorials
• An amazing demonstration of what simply adding CSS to a plain old HTML page can do! See hundreds of different page designs all based off the same HTML source, at The CSS Zen Garden
• Validate your CSS code with this tool from W3C
• A showcase of CSS designs, CSS Beauty