I’m working on a redesign of my homepage and completely forgot how much screen real-estate is available within a browser to display your website. A quick Google serach told me the following:

Screen resolution – available in browser
640×480 – 600×300
800×600 – 760×420
832×624 – 795×470
1024×768 – 955×600

Original forum post:
Available browser space for different screen resolution

Some interestion information about browser usage, including most common screen resolution, etc can be found at W3C’s Browser Information page.