One that doesn\'t require the following:
http://960.gs/
This one can be used for a 3-column layout (and for various other layouts). Personally, I don't think it's a great idea to use divs for everything, but it's simple and well .. it works.
edit: For a 100% width layout http://www.alistapart.com/articles/fluidgrids/ may help, but I'm not sure if this kind of layout still qualifies as "simple".