For all of you Terragen lovers out there I have found a great program that you can use in conjunction with the Terragen program! (Actually I didn't find it - the good folks at Renderosity's Terragen Forum recommended this program.
It is a separate program that lets you create and modify 3D terrains that you can then import in Terragen. You can build some stunning-looking terrains with this program! I'm still learning it myself and you can see my progress so far:
You see, with using the Terragen program you can still create some good-looking terrains like so:
But with the World Machine Program you can also import .bmp files into the World Machine Program and add different "filters to it and get some very good looking effercts.
Here is currently a work-in-progress that I am currently working on:
You can find out more about World Machine (including a free download of the program) by clicking here!