Desktop Earth is a wallpaper generator for Windows. It runs whenever you're logged on and updates your wallpaper with an accurate representation of the Earth as it would be seen from space at that precise moment.
Day and night is accurately represented depending on the Sun's overhead position (which depends on both the time of day and the day of the year) and both the snow cover and the foliage changes with the seasons.
Images are created from high-resolution textures (2560x1280) so it's perfect for that QSXGA display.
An image is generated every month to accurately depict snow and foliage changes, and the night view is simply stunning.
If you just want to stick with one view of the earth, there is a huge stash of wallpapers in the install directory that can be used permanently without being connected to the internet or having Desktop Earth installed.
My Desktop view:
(Click for larger view)