This and the hex grids get a lot of views on Amit's site, but he has a lot of neat things on there.

He just finished mapgen4: "Paint your own mountains, oceans, and valleys. It will procedurally generate rivers and biomes based on wind, evaporation, and rainfall. Rendered in 3D to look like hand-painted 2D."

Check it out if you're interested: https://www.redblobgames.com/maps/mapgen4/