I really enjoy the mastery of modern CSS layouts using a grid based on solid design principles, pre-existing the Web. My two favorite are 960.gs and Blueprint, so I’ve taken the elements that I like best about each css framework and mashed them together into one. 960.gs has both 12-column or 16-column grids ready to go. While Blueprint has more comprehensive element styles, a 18px baseline grid, and a few additional settings (e.g. the “pull” class to break outside the grid). Below are the sample pages from both CSS frameworks:

1. Demo of 960 pixel Grid (960.gs 12-col & 16-col)
2. HTML elements
3. Blueprint Sample Page