...and Bryce 5.5 is free from Daz, or Cnet...see posts above...not only do you get terrains....you get foliage..;) Terragen's good too...it's where I started out.

Also, should you want to do some modeling of buildings, objects, props, etc., there's Blender, Wings, both free...

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)