I found this thing on the asset store (I am not the developer of it), but it's probably the coolest terrain-related unity extension I've ever seen. http://u3d.as/content/stu-assets/terrain-mesh-blending-tool/30h $125, but worth every penny. This is impressive, AAA-level stuff. StuAssets, where the heck are you and why aren't you pimping your kit?!