Recently I came across one of the coolest applications of augmented reality ever. Couple of researchers from UC Davis Center for Active Visualization in the Earth Sciences have developed a sandbox that acts as a real-time interactive, topographical map with contour lines and color shading. When ever you change the topography by moving the sand, the new isolines will be projected on the sand.
The project uses Microsoft Kinect camera coupled with topographic visualization software and a 3D data projector. The Kinect takes stereoscopic images of the topography of the sandbox and sends the data to a computer. Researchers applied the Vrui VR development toolkit in conjunction with the Kinect 3D processing framework to compute the visualisation from a specific point of view of the data projector fixed above the sandbox.
If you see one of those in a science museum somewhere in the world let us know!