The moons of Jupiter (well, the 4 major ones) are in their own right, a Solar System within a Solar System. There is volcanically explosive Io; Europa with its cracks and ridges hinting at its huge internal ocean; Ganymede the largest moon in our celestial neighborhood and Callisto one the most heavily cratered bodies we have anywhere. The 4 moons are also called the Galilean moons as they were discovered by Galileo and have since been revealed to be more fascinating than most planets are. The images below represent what I think are likely the best representative images of these places that can fill a 2560x1600 screen. At this size, the details are quite impressive… do take a look even if you can’t make use of the images as wallpaper images.
The Europa image is actually a render created by Tayfun Öner as not that many satisfactory images exist of a full globe Europa. Many great images exist of Ganymede but most are low resolutions, this image was stitched together by Ted Stryk of www.unmannedspaceflight.com. The other two are officially released NASA composites.