I've been recently playing around with Terragen, a fractal landscape generator which is quite easy to use for a beginner like myself. It has a wide following as well. And, although its is mostly used to generate static pictures, the community has started using it to generate planets and fly-overs.

I created the above picture in about 10-15 minutes. Its amazing how far this has come. I think I created my first fractal mountains on a silicon graphics box in 1993. It was just a crude wire rendition but I was so excited even then at the potential for realism.