Desktop Earth is a utility that generates wallpapers from satellite imagery of our home planet. It runs from the system tray, continuously updating the wallpaper to reflect changes in sunlight, foliage and even snow cover.
Automatically resizing images to match the Windows PC's native resolution and reduce the load on the system, Desktop Earth takes care of itself for the most part. However, the user can control the level of cloud cover, which time zone the wallpaper is centered on, if night lights appear on the dark areas of the satellite images, and of course, the frequency of updates.
Needless to say, DE (latest version 2.1) requires a permanent internet connection. You can download the utility here.