I'd suggest that your central column should be (approximately) half the screen width, up to a maximum. If you have one sidebar, you could go a bit wider; with two sidebars, a bit less - depending on what you have in the sidebars, of course.
But, please keep it a proportional value instead of a fixed one.
Like many others, I've spent the money (at home) or begged the boss (at work) for a nice high resolution screen, or two, so that I can read more at one time. Fixed width layouts penalize both those with higher resolutions (wasted screen space) and those with lower (horizontal scrollbars).
To illustrate ...
My laptop runs native resolution 1920x1200 - nice, clear, plenty of room, lots of space to put content for reading.
But, when I browse to a site using a 960 pixel fixed width, I have one of two problems.
Either I maximize my browser, leaving half my screen completely whitespace:
Or if I put two browsers side by side, the content is clipped and I have to monkey around with a horizontal scroll bar as I read:
The kicker is this: it's entirely unnecessary to cause these problems. It's perfectly possible to create fluid width layouts with constraints to prevent things going too wide or too narrow (there are plenty of sites that do just this).