File: SASS_REFERENCE
Sass - Syntactically Awesome Stylesheets
WP Separate CSS « WordPress Plugins
WordPress Bootstrap CSS « WordPress Plugins
Custom CSS Manager « WordPress Plugins
CSS3 Image Styles – Part 2
Measuring and sizing UIs, 2011-style — CSS Wizardry—CSS, Web Standards, Typography, and Grids by Harry Roberts
Less Framework 4
Frameless
The Art & Science of Folding CSS Code | Perishable Press
Powerful New CSS Techniques and Tools - Smashing Magazine