Did you like the wallpapers of Canadian scenery I showed the other day, that are already on your Windows 7 machine and just need to be selected? Would you like some more? Go to http://windows.microsoft.com/en-US/windows/downloads/personalize?T1=themes and scroll down past the Coke and Ferrari and so on to find more lovely scenery. I copied mine into the folder that was already the source for my desktop wallpaper rotation.
I think the Northern Lights is my favourite at the moment.