jQuery - YUI 3 Rosetta Stone
Very useful when scripting for Squarespace
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.
The Grid System
The grid system is an aid, not a guarantee. It permits a number of possible uses and each designer can look for a solution appropriate to his personal style. But one must learn how to use the grid; it is an art that requires practice.
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
The Great Typekit Table – Sleepover
Useful for Typekit users
Safari Reference Library
The Safari Reference Library provides detailed information for web developers on iPhone, iPod touch, Mac, and PC. These resources include guides and articles, API reference documents, sample code, release notes, and technical notes. Use these resources to learn about Safari's developer tools, visual effects, HTML and CSS support, JavaScript and DOM support, and other features and technologies. The library is organized by Topics and Resource Types
12 Useful and Free Downloadable Web Design Books
Handy references by Speckyboy Design Magazine
Daring Fireball: A Liberal, Accurate Regex Pattern for Matching URLs
A common programming problem: identify the URLs in an arbitrary string of text, where by “arbitrary” let’s agree we mean something unstructured such as an email message or a tweet.
Assistive Technology: a video tour of accessibility
Video introduction to assistive technology and how users use them