Bourbon Sass Mixins Library
A simple and lightweight mixin library for Sass. Bourbon is a library of sass mixins that are designed to be simple and easy to use. No configuration required.
Home - Scalable and Modular Architecture for CSS
A brilliant and inspiring book. Not only useful, but fun to read too. Full of good tips and ideas. I love the approach.
Vendor-prefixed CSS Property Overview « Peter Beverloo
25 Useful Html5 Cheat Sheets and Tutorials For Web Developer
11 Free Tools Important For Web Developers
Best Collection of Useful CSS Tools for Developers
Responsive Web Design: Helpful Articles, Techniques & Tutorials
12 Useful and Free Downloadable Web Design Books
Handy references by Speckyboy Design Magazine