Attached Link: http://worldwind.arc.nasa.gov/features.html

world wind is free of charge, download it from the nasa website. i think the idea was just to use it as textures or alphaplanes not realy like using dem files in other words but i could be wrong i havent realy checked out worldwind myself more then a few minutes (its a seriously cool app just that i havent had time) so it might even be able to spit out dem files or its possible to use the images to build terrains what do i know :)