I've recently come across yet another amazing new game. This is a 3d global simulator, creating a 1:1 scale of the earth with amazing terrain detail. It's still in Alpha but the sheer scale of this game is breathtaking. I've already purchased the alpha (half price, get future updates for free) you can place objects, roads, drive vehicles on land, in the air, and underwater. (the underwater is fully textured and detailed as well!)
Here is the demo link
http://www.outerra.com/forum/index.php?topic=637.0
You can't do nearly as much in the demo (I think you can drive around a car, that's about it) but you can still fly the camera around looking at all the detail. I believed this was worth $15 to support the developers as they have a very awesome thing going here.