I use 1280x800, but 1024x768 is what you should design with in mind because that is indeed the usual resolution these days, at least at minimum. A larger design will cause people to have to sidescroll, which is disgusting, especially if you have to downscroll to read stuff on a site. A smaller one for 800x600 would look a little too small, but even a midget design for a site is better than a too large one.