Fractscape builds fractal terrains by setting a few parameters quickly. I am not sure how useful this is, but when I tried it, I did spend quite a bit of time with it – its kinda fun to check out. Fractscape can export terrains for game engines or other uses, or just wandering around. You can load your own textures, and build high-res terrains out of low-res heightmaps, or randomize everything and just try and see.
