Ive been playing around with fractal algorithms to create heightmaps for ottd. Especially the 1 height difference limit makes it hard to have nice looking mountains (with peaks) in the game. I wrote a map generator using the plasma fractal (random midpoint displacement), while forcing it to make water edges to get some big continental shapes. Tell me what you think, I myself am quite happy with how mountain ranges look while still enough flat land to have a playable scenario.
Ingame example: The GUI should be really intuitive. Select some parameters, seeds and generate until you see something that suits you:
The results will be saved in a directory called 'output' and consist of both a coloured image and a greyscale image. The coloured looks nice, and the greyscale is for use in openttd.
If you encounter some nice maps/seeds, please share them here with the rest

cheers
zooks
edit (09/04/13): added python source
edit (11/04/13): added link to png library
edit (18/04/13): uploaded the gui