I have a new desktop background, at least at work. A program that automatically generates a view of the earth, or any other planet, updating automatically as the planet rotates relative to the sun. You can also map realtime cloud images onto the view, producing a realistic simultation of the earth from space.
You can produce some fascinating images like this. My own desktop is currently a view of the earth from about 20 degrees south of my own position in London, England. I have a screenshot of it as it is right now. You can use it to tell the time and weather too, just looking at the areas that are in daylight. The areas that are dark are equally fascinating, as you can see the millions of lights lighting up crowded places like England, while areas like central Africa are pitch black.
Haven't decided whether to keep the clouds yet. they are really interesting, but they tend to blot out some of the places that are more interesting to me, like the whole of England for starters.
One downside I found was that it was a real pain install and configure, being mainly designed for Linux gurus and patched for lowly windows users afterwards. Still, it works really well one you're done, so it's worth the effort. I also used the XPlanet Control which is linked from the main site.

The software is open source, and is available from it's website at sourceforge:
Xplanet
WXplanet for Windows