This world generator uses fractal terrains and various simulations to generate highly detailed random map data. It is open-source and licensed under the GNU General Public License v3, with some sections also available under the MIT license (at your option).
There's a video and more screenshots.
This is a prototype; stay tuned for updates!
Update: Now public domain on GitHub
Rendered Final Map
Wind and Rain Simulation
Experimental feature: using wind & rainfall data to render clouds.
Hero Extant Wallpaper, 1440x900 (2D landscape render).
You can also contact me directly - I make an effort to reply to every e-mail.