Chris Anderson came up with a kid-hackable UAV, the GeoCrawler 2, using an RC aircraft and a Lego NXT:
Features: In GPS mode, unlimited pre-programmed waypoints, with programmable options such as circle and hold. Ability to integrate other sensors, such as ultrasonic, compass, gyros, accelerometers, or barometric pressure (altitude). With optional bluetooth cellphone integration, control via text message, including dynamical-changed GPS waypoints, “come home” and “circle” commands, etc.
Instructions for the GeoCrawler 2 project are available at Chris’ DIY Drones site, a growing social network for folks interested in building unmanned arial vehicles.
This is really an underexplored area of amateur robotics, primarily because it’s been so cost prohibitive until very recently. I’m excited to see what people come up with over the next year or two. I expect it will be mind-blowing.