The Virtual Terrain Project is an open source three dimensional modeling software that is available for download upon request. I can’t speak for any of its features since I haven’t used it yet but the project’s site has a number of useful links for data sources that even non-3d modelers would find useful, particularly remote sensing and digital elevation data. Much of the focus is on the United States but there are extensive links to data from the rest of the world.

By way of Cartotalk