What is the most common...?

[Fishbusters]

I was wondering if anyone here knows or knows how to find out what is the most commonly used desktop size? I know mine here and on the laptop is 800X600 pixls and I think work is the same. My wife was recently looking for pictures to use on the laptop because she likes to change it ever so often and this thought crossed my mind when we found out that many of them would not fit.