Which of the three sites in your sig are we talking about? The first one seems to be the only one sporting three columns, and on none of the pages I've scanned quickly I could find a strong reason for a third column.
I'd get rid of it in favour of a more flexible layout based on a grid that allows you to add or remove columns and redistribute their widths based on the specific requirements on each page while still maintaining a cohesive look and feel.
Khoi Vinh has addressed using grids in layout design
on a number of occasions; recommended reading if you want to now more about grids.
Much more about the topic on this page