Some handy resources for warming up on CSS:

Popular recommendations:

• A List Apart
• The AnyBrowser Campaign Design Guide
• Glish CSS Layout Techniques
• WebSiteTips CSS
• Data Tables & CSS Gallery

W3C Tips

• W3C Accesibility Features for CSS
• W3C Recommendations for CSS - Level 1
• W3C Recommendations for CSS - Level 2
• W3C CSS Validation Service (Tool)
  

SitePoint Articles

• Fancy paragraphs with CSS
• CSS is Easy
• What is Liquid Design
  
• Introduction to CSS shorthand

CSS Galleries

• CSS Zen Garden
  
• CSS Vault
  
• CSS Beauty
  
• CSS Top Sites
  
• Stylegala Gallery
• Arcsin Templates
• Solucija Templates
• Free CSS templates
• CSS Templates & Tips
• Smashing Magazine Compilation
• Dynamic Drive Layouts
• Layout Reservoir at BlueRobot
• Little Boxes at the Noodle Incident
• Complexspiral Demo (history)

Trends

• Stop Design
• SimpleBits
• Real World Style – Mark Newhouse
• Design Interact Site of the Week