A Responsive CSS Framework For Rapid Prototyping – Centurion
Centurion is a CSS framework, built using SASS and CSS3 media queries, for creating (mostly prototype) layouts that behave good on all devices.
It includes a 960px grid (that scales down to 320px), can handle image scaling and has a navigation with desktop and mobile versions.
There are also styles for CSS-only buttons and tables. The framework is easy to learn and customizable (thanks to SASS).