OK, here's my second attempt using RobA's tutorial. I tried using the alternative method of doing mountains that he created the video tutorial for, and experimented with some other stuff.
I pretty much like the way they turned out other than there being to much space between them (I was worried about overlapping, and really didn't need to be ), and maybe some 'banding'.
The off-colored moutains with the red at the peaks are supposed to be Volcanoes. The sandy-colored areas were done using the 'dunes' brush.
The chasm and the crater were done using the same techniques as the mountains, only inverting the bump map. The crater isn't that great, but I think the chasm turned out OK.
As always comments, critiques, etc. are welcomed.