Just Cause 2 has, in my mind, a phenomenal landscape. Snow-capped mountains, rugged stone valleys, beautiful emerald valleys/hills/mountains, desert area, etc...
This online representation of the world (using tiles of the in-game map) is also interesting: http://www.maplib.net/fullmap.php?id=8630
It uses the "Avalanche Engine 2.0"...here are a few in-game action shots: http://www.google.ca/images?q=Avalan...w=1680&bih=897
The in-game map and the in-game real-world match up very nicely.
Alas, no map editor yet....but fingers are crossed here.