Z-BRUSH
You can download a free evaluation of Z-Brush here.
TERRAGEN
AUTOCAD
Below here are pictures made by my friends but put onto my site
Copyright © 2002 Christopher Hohmuth
These images were made using only Adobe Photoshop 7.0.
Below here are the terrains I have made using Terragen.
Below here are the few 3D images I've made using AutoCad.