Terragen
Using a landscape generator with controllable parameters, I was able to create extremely varied terrain shapes that could then be rendered into a photorealistic picture. You can look at some of my productions or learn from my tutorials.

Bryce 5.5
A 3D landscape modeling, animation, and rendering software package that is extremely fun to create with. Look at my some of my renditions as I explore the imagination Bryce allows one to go to...

Apophysis
This freeware fractal flame editor for Windows will keep you busy creating masterpiece after masterpiece. Look at what I produced and enjoy. Tutorials available...