What resolution should I design for?
Start with flexible design. Stop trying to achieve DTP. -- Steffi
Design for all of them by making your design independant of any resolution. Don't be fooled into thinking that the World Wide Web is only about web browsers on personal computers. The World Wide web is much bigger than a piece of software and a monitor. Search engine spiders and indexers are very simple browsers, with no monitors.
Primarily, avoid anything that imposes a fixed width requirement. Of course, some content, mainly images, need to impose such requirements. Try to keep them below 400 pixels horizontally, unless the content really needs more. (Something like 400 pixels is a fairly nice browser window width - one can then have two or three windows open on the screen simultaneously.)
Web TV can comfortably handle a table 544 pixels wide.
There is a myth that page dimensions are stuck at the size of the screen. They are not. A desktop of 1280 by 1024 or bigger is usually adopted to fit more open windows on the desktop, not to make one window bigger.