A great source for terrain generation information is the Virtual Terrain Project (http://www.vterrain.org), which has sections on elevation models, ground detail, rendering, data sources and formats, scenery, software tools, and plants.
GameDev.net has a collection of good articles about landscape modeling at http://www.gamedev.net/reference/list.asp?categoryid=45#88.
Though my focus is on gaming, terrain creation is used by simulation and GIS applications. A popular file format for geographic data is the Digital Elevation Model (DEM), which represents grids of regularly spaced elevation values. The USGS produces five primary types of DEM data, which represent different levels of geographical detail: 7.5-minute DEM, 30-minute DEM, 1-degree DEM, 7.5-minute Alaska DEM, and 15-minute Alaska DEM. Here are some useful DEM links:
Terragen can understand various USGS and NASA file formats when used in conjunction with plug-ins and/or other terrain-based applications, such as 3DEM. This makes the data available to
Terra3D once saved as OBJ and JPG files.
The j3d.org code repository (http://code.j3d.org) contains a DEM loader in
org.j3d.loaders.dem, but it's poorly documented with no examples of its use. However, the loader is used as part of the GeoSim application, to display ...