Need a scenery generator? Look no farther than Terragen. Currently it supports both Windows and MacOSX and is on version 0.9. This version is free as will be Terragen 2, which is in development. The basic idea is that this can randomly generate photorealistic environments or actually layout the environment itself.
Terragen has been used in multiple mediums including print, multimedia, film and online. What’s interesting about Terragen 2 is that it not only is it complete rewrite, it also supports vegetation. This means that you can now have trees and other types of things in your actual environment that makes it all the more interesting.
There is registration involved if you want some extended capabilities or if you want to use it for commercial use. In this case, you would have to purchase a $99 registration. Outside of that, personal use and nonprofit use is free and only limits you to certain resolutions and some other features depending on which operating system you are currently using.