There are a number of examples and libraries out there you can search on - a couple already listed (A List Apart is a must read).
I've used the Yahoo User Interface Library (YUI) on my last couple of sites and really like it. Yahoo completely supports it and it's quick to understand and use. Here is there CSS for Grids, which allows you to format your page into as many columns and sections as you want.
YUI is nice because you don't have to reinvent the wheel for the foundation of your site, and they do all the work of making sure their foundations work across all browsers. And best of all, it's free.
