Something that’s been a pet peeve with me, is that too many sites use 960 pixels, no matter how much content a site has. I understand it works great for at 1024 width resolution and there is nothing wrong with white space. But I’ve seen too many sites use it with no thought. Often times you see a site and there is only a paragraph or 2 in the left and 1 in the right and the design doesn’t utilize the whitespace and lack of information on the page. Does this mean use 760px (good for 800 width resolution)? Personally I think if you want your site to stand out a bit, you should use a smaller size width or a different width size than those 2 standards, but again it depends on how much content you have and how your design handles varying amounts of content.
Now about centering pages, I know resolution widths these days can be huge on wide screen monitors; However if you want to set your site apart a little, place it slightly off center. Depending how off center you place it, you may want to balance it off with a subtle background graphic or something on the other side or slightly on the opposite side. I’ve done this on a few sites and it really seems to make the site seem fresh, compared to the 960px landscape. But perhaps you know of the 960 grid system CSS framework and think its the only way to design.