CSS is the essence of a web page. Its the beauty of the page and is really useful for Ajax oriented applications.

There is a useful tutorial that I found out and assume that it will  be beneficial for both the people who are getting started to learn CSS and for those who want to refer the different layouts and styles. I have mentioned below the resources , have a look at whatever you feel to be appropriate.

CSS

• Finding Your Way at W3C
• CSS-1 Reference
• Updates to CSS-1
• CSS-2 Reference
• Updates to CSS-2
• Selectoracle – Enter CSS Style Sheet and All is Explained
• Websitetips.com – CSS Section of Resources and Links

Learning CSS

• W3 Schools
• CSS101: Beginners Course
• HTML Dog CSS Beginners Guide
• NWE Help’s CSS DIV Instead of Tables
• The CSSShark Answers FAQs
• HTML Source’s Introduction to CSS Stylesheets
• Web Page Design for Designers – CSS From the Ground Up
• Westciv’s CSS Hands on Tutorial
• Digitalweb’s CSS 101
• The Web Developer’s Network
• CSS Vault
• Mezzoblue’s CSS Cribsheet

Style Guides

• NYPL Style Guide
• Rich-In-Style Guide
• W3c’s Web Style Sheet Guide
• CSS Tutorials from BigBaer.com
• Adding A Touch of Style

CSS Expertise and Examples

• Eric Meyer’s CSS Edge
• Eric Meyer on CSS (site based on book)
• CSS Zen Garden – the art of the possible in CSS
• A List Apart
• CSS Design Experiments
• Style Gala
• Open Source Web Design

Layout Resources

• Position Is Everything
• Position is Everything’s Complex 3 Column – Perched on a Lily Pad
• Position is Everything Piefecta Ridid 3-Column Layout
• A List Apart’s Flexible Layouts with CSS Positioning
• Glish.com CSS Layout Techniques
• Creating Liquid Layouts with Negative Margins
• Faux Columns: Column Stretches
• Imaginary World’s Internet Brain CSS Layout Templates
• Brainjar’s CSS Positioning
• CSS Examples from W3 Schools
• Stopdesign’s Making the Absolute Relative
• ClevaTreva Designs’ Bug Proof CSS Style Sheet Generator
• Two Columns with Color
• Mako’s CSS Positioning
• Toss Out Your Tables: CSS Is Your Scene
• Liquid CSS Layouts – Design Alternative to Table Based Websites
• The Layout Reservoir
• MaxDesign’s CSS Layout Examples and Guides
• Eric Meyer’s Articles on CSS
• CSS Layout Tutorial
• Mandarian Design’s CSS Examples, Tips, and Tricks for Bloggers and More
• RuthsarianLayouts’s CSS Layout Templates and Tips
• CSSLayouts Tips and Techniques
• Ruthsarian Layouts Examples
• WebColor’s WebMaster Kit for CSS Colors
• CSS Tips and Tricks from Camera on the Road
• CSS HowTo at Intensivstation

Boxes and Design Elements

• The Noodle Incident Tutorials on Boxes
• Maxdesign’s Colored Boxes and CSS
• CSS Sketchbook
• Mandarin Design’s Boxes and Borders: Box Tips and Tricks
• Tantek Advanced CSS Examples
• Basics of Element Boxes, Margins, Padding, and Stuff
• CSS Border Image Text Box Styles
• CSS Experiments With Design Elements
• HTML Color Codes Chart
• HTML Color Codes Color Picker

Hope the above links empowers you to learn as much as you can about CSS and different tips and tricks.