The Yahoo! UI Library's Grids CSS framework might seem hard to grok at first, but I've been using it for the past year on a commercial project and find that it's solid for liquid CSS layouts. The grid builder helps to visualize what's possible and view the rather obscure naming conventions they use in CSS classes.
The framework offers four preset page widths, six preset templates, and the ability to stack and nest subdivided regions of two, three, or four columns.