Animate.css
The ultimate CSS tools for web designers | CSSmatic
Gradient generator, border radius, noise and box shadow
Ultimate CSS Gradient Generator - ColorZilla.com
Useful to generate IE 6-98 and 9 gradients (filter or svg)
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.
ProtoFluid - HTML5 and CSS3 Web App Prototyping
Test your @media queries and web app on various screen sizes