It's been a while since I have seen something that has truly changed the way I look at technology... But a few of the projects designed by Johnny Chung Lee, a Ph.D. graduate student at Carnegie Mellon's Human-Computer Interaction Institute, are quite remarkable in their ingenuity. While many of his projects are applicable becuase of their use of products that are readily available, two projects of his stand above the rest. If you haven't seen these yet, make sure to check out his demonstrations of "Head Tracking for Desktop VR Displays using the Wii Remote" and "Foldable Interactive Displays".
Head Tracking for Desktop VR Displays and other Wii Projects
Projector-Based Location Discovery and Tracking with Foldable Displays
About Johnny Chung Lee