WinEarth

WinEarth sets the screen background to an image of the Earth, as seen from your favorite vantage point in space, correctly shaded for the current position of the Sun.
The program has a variety of options, which are accessible from a dialog box. Some of the options are shown in this screenshot:

The current version of WinEarth (1.02) for Windows NT 4.0 and Windows 95 is available as zip file here (1.7MB).
The setup program installs the binary and optionally the source files.

Quoting Kirk Johnson, the author of Xearth: "There are a number of improvements that I'd love to make, but I really should be working on my thesis instead of hacking on this". I am working on a screen saver version of WinEarth (thanks to Zem Laski for the idea). Actually, it is running on my PC as alpha version already, but it still needs some improvements before I'm comfortable with releasing it.

WinEarth was ported from the well-known Xearth program. I am grateful to Kirk Johnson to come up with this great program. Kudos also to all the other guys who contributed to Xearth.
I borrowed some Windows code from Paul DiLascia's excellent C++ column in Microsoft System Journal (now called Microsoft MSDN Magazine.)