First of all, I hope it's not improper to do a thread like this, and I hope it's in the right place.
I've created a 1024×1024 heightmap featuring a star-shaped continent, with interesting yet gentle hills. Canyons allow (most) rivers of the interior to flow to the sea, and also provide opportunities for dramatic bridges.
This was created by combining output of a few runs of a custom noise generator I created, then cutting the canyons manually in an image editor. It went through a few rounds of testing to fix some river basins where the game failed to find paths for rivers.
This heightmap is available on Bananas as "Star Continent".
Preview-size images below; see attachments for full-size screenshots.