Customizable & Responsive Grid System: 34Grid

34Grid is a grid system for responsive layouts which is based on "equally distributed columns" for each row. There is no built-in CSS reset (so that you can use your own) and there are rules for handling images + video. Also, there is a "how-to" in the resource's website for handling social widgets which can be very handy.

Customizable & Responsive Grid System: 34Grid