Please do not make your website width 800, 1024, or 1920 as others have suggested. First of all, the 1920 suggestion is terrible for an absurd amount of reasons.
Those may be good target computer resolution widths, but you want your actual site a bit smaller to account for the scroll bar. It's crappy to force a horizontal scroll bar when just a few pixels could have eliminated it.
A common size for accommodating 800x600 is a 750px width. Since 800 width is very tiny, websites that are made to be compatible for this resolution don't care about outside whitespace. A common size for 1024x768 is 960px.
Just three years ago you would have alienated 10% of your users by not accommodating 800x600, today that number is less than 1%. Around 20% of people still use 1024x768, so really for a general use website you don't want to go above this.
Even at larger resolutions, wider websites are not always desirable. You can only put around 80 characters per line before readability goes out the window. Even though a lot of people have 1920x1080 monitors now most probably don't want to see a website that wide.
My vote is
960.
ref