Yeeehaaaww! I’ve been waiting for this major update for months!
Terragen is a program that allows graphic artists to generate photo-realistic scenery. It’s a little tough to use, but can make some great stuff. It can even upload real 3d data like what the mars rovers send back, and map that for you. Quite a nice program for the cost: free. Some examples of Terragen’s power (these have post-processing with The GIMP ):