terragen been around a long time and simple and fun to use and can be quite effective.
Bryce is another. If you want to go up a few notches get hold of vue infinite. Its not cheap but it can integrate with other applications and it has all kinds of decent GI and even a full on eco system generator.
Nice post Andy.
I can't remember if terragen has primitives with it or if that was bryce. Not played with either for a very long time. These progs were what got me into 3ds max