960 Grid System
Here's another CSS framework for grids. It could prove to be very useful for wireframing.
Toast | A simple CSS framework
This is interesting, not because it’s yet another grid framework (which I never use anyway) but because of the way it’s doing layout: with border-box and inline-block, rather than floats. If you’re only serving up your layout styles to browsers that support media queries (which would discount older versions of IE anyway), this could make a lot of sense.