Terragen

Terragen is a freeware scenery generator program for Microsoft Windows and Apple Macintosh developed and published by Planetside Software. It can be used to create renderings and animations of landscapes. It is popular among amateur artists, which can be attributed to it being freeware, its intuitive interface, and its capability to create photorealistic landscapes when used skillfully. It can also use DEM files, and other graphic surface maps for rendering. The terrain is generated from a two-dimensional heightmap. The program contains facilities for importing and exporting heightmaps to images, for use in other programs.

Homepage: http://www.planetside.co.uk/terragen/