EarthDesktop

Since Compiz 0.7.6, desktop deformations are possible: Sphere and Cylinder. I cut a cylindrical projection of the earth into pieces so that it fits on the four sides of the cube and the caps. Just unzip the file and use Compiz-Fusion's ccsm to put the files in the right places.

Edit 1:
Many commenters don't know how to put four different wallpapers on four different sides of the cube. Here's a link to one of the methods:

http://forum.compiz-fusion.org/showthread.php?t=6199

My package doesn't contain an installer. Just untar/unzip it and put the files somewhere on your harddisk. Then, open up your Compiz configuration application (ccsm, probably) and point to the right images.

Edit 2:
The image used isn't that detailed. If you find a better one, you can do the same trick with the GIMP. Just be sure it is a cylindrical projection (a rectangular (2:1) shot with huge poles). Then copy the top 25% into a new picture and do Filters>Distorts>Polar Coordinates. You might want to keep this open, because you need to rotate it to fit the middle parts. Now do the same for the bottom 25%. This gives you the cube caps.

When everything goes well, you're left with a 4:1 middle part. Just cut it into four equal pieces. Now you're stuck with square (1:1) desktop images, so you might also try to make desktop images with the right aspect ratio. This however results in bigger polar pieces and distorts the globe texture. Feel free to experiment and post me the right way to slice'em.

0.1 initial release