Stylish is to CSS what Greasemonkey is to JavaScript. Stylish allows you to easily manage user styles for the application UI, all websites, or only certain websites. Stylish is better than using userChrome.css/userContent.css because styles are applied immediately instead of requiring a restart.

[Read More About the Stylish Extension!]

For more help, check these out...

• Redesign Google
• New Digg, Old Style
• Gmail Redesigned (plus some more neat features)