Atlas is a Java program written by me that is intended as a Map Generator for Civilization 4. But if you are as fond of maps as I am, it's good in its own right for just producing interesting pictures. Presently version 0.43 is available for download. It's pretty functional, and it generates fully playable maps.
Atlas can generate maps that are bigger, more varied, more realistic and more customizable than those from the standard map generator, giving the user control over every single parameter, and (optionally) providing a preview of the map as well.