Hey, i just played a liitle around with a programm called terraform(gnome-program), that can create very interesting heightfield maps.
With the combination Blender/Terraform this came out
(it’s just an early WIP so please don`t blame me on the textures and the lighting 
!!).
I just want do demonstrate what’s possible with this two neat/free programs ;-).
the Heightfieldmap:
rendered pic low res:
and a HiResPic:
http://www.olafarnold.com/crazyterrain.jpg
well, let’s see what i can do in the future with it… :-).