I have to pay tribute to Torben Mogensen, who I've never met. I used his program (available here: http://www.diku.dk/hjemmesider/ansatte/torbenm/Planet/ ) to create the planet Elpis.
His planet generator is a CLI-based program, but very powerful. Importantly, although based on random seeds, it has a find function so you can put in elements of how you want the planet to look and it will find a seed to produce something close to it. I explored a fairly large number of seeds until I was content and modified some parameters until it was what I wanted it to be. Usefully, it allows you to zoom in on areas as well.
GIMP was used to manipulate t