Title: Unity 3d game engine terrain toolkit
Vendor: Unity3d
Web Site: toolkit: http://unity3d.com/support/resources...errain-toolkit after you have the engine
Type: Heightmap, 3d
Focus: General/3D
Platform: Windows/Mac/Linux/Web Based
Price: $0
Description:
The Terrain Toolkit is an integrated set of tools for the Unity Editor which is designed to streamline and improve the workflow involved in creating realistic terrains for games. The toolkit enables the creation of large scale, realistic and playable game worlds within a very short time span.

Examples:
Creating heightmaps http://vimeo.com/album/150503

Here's an example I made from the game Ultima Online's map in 3d:
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I can make scalable 3d maps of just about any feature/bay/mountain range based off a google image in around an hour for the base, it takes a little longer to paint on the textures, but definitely far faster than hand forming terrain...