Here are some more.
Leveller
http://www.daylongraphics.com/products/leveller/
Great program for serious application or just fooling around
ImageSynth2
http://www.luxology.com/imageSynth/
Excellent for creating seamless textures from ANY image
MicroDem
http://www.usna.edu/Users/oceano/pgu...m/microdem.htm
Free - useful for opening DEM (Digital Elevation) files
Texture Maker
http://www.texturemaker.com/news.php
Flaming Pear
http://www.flamingpear.com/products.html
Photoshop plugins. India ink and Lunar cell are pretty cool
The heavy weights ...
Global Mapper
http://www.globalmapper.com/
The Daddy ...
VNS3
http://3dnature.com/vns3.html
Excellent! good for ecosystems - massive learning curve but worth it
CityEngine
http://www.procedural.com/
Pain to use ... has some cool features such as importing OSM (Open Street Map) data
