Links to CSS Websites and Books

A List Apart - Code and design.
Smashing Magazine's CSS tips
CSS Basics
CSS Tricks
cssreference.io
DevDocs - Multiple API documentation.
HTML Dog - CSS and HTML Tutorials.
Html5please - Look up feature compatibility.
The Absolute Minimum every software developer must know about Unicode and Character Sets - Joel on software.

Tools

W3C CSS Validation Service
W3C Link checker - looks for issues in links, anchors and referenced objects.
ArchiveReady- archivability evaluation tool.

CSS Tidy online + util
Clean CSS - CSS Formatter and Optimiser.
CSS minifier - Make CSS files smaller.

Web Page Performance Tests:
Gtmetrix
PageSpeed Insights (Google)
Pingdom
WebPageTest
YellowLab - Test to help speed up heavy web pages.

BrowserShots - Preview a design in multiple web browsers.
CSS Typeset - Generate CSS rules online.
Fiddler2 - Web debugging proxy for any browser.
FontAwesome - Web icons embedded in an open source font.
HowToCenterInCSS - a gazillion ways to centre.
jsfiddle - Test your code online.
Kotatsu Table HTML Generator
Sass - an extension for CSS3 - nested rules, variables etc.
tSelenium - Automate browsers.
SortTable - Make all your tables sortable.
Specificity Calculator - Change the selectors or paste in your own.
SubtlePatterns - Tileable textured patterns, free to use.
Tufte CSS - Use the design ideas of Edward Tufte.
WebPageTest.org - Free website speed test from multiple locations around the globe.

Resets

Eric Meyer CSS Reset
YUI CSS Reset

Browser compatibility tables:
FindMeByIP - HTML 5 & CSS 3.
CaniUse - HTML 5 & CSS 3.
html5please
Common fonts to all versions of Windows & Mac equivalents

Frameworks / Templates

Bootstrap - from Twitter.
GridByExample - Examples of Grid
CSS Layout cookbook - Mozilla

Where to file CSS Bug Reports

BugZilla
Microsoft connect
Chromium issues
Open Radar - OS X/Safari Community bug reports.

Recommended Books

Book links on this page are in association with Amazon.com

HTML and CSS: Design and Build Websites
by Jon Duckett, 1st Edition, Nov 2012

CSS Mastery
by Simon Collison

“Fashion fades, only style remains the same” ~ Coco Chanel