The University of Pennsylvania's GRASP Lab created these UAVs to be light and maneuverable. They measure about 8 inches (20 cm) in diameter and weigh 60-70 grams.
Professor Vijay Kumar explained how they work at a recent TED talk. There is no GPS system guiding their movements. Instead, they are equipped with a Microsoft Kinect and a Hokuyo laser scanner. They can actually be sent into a building and create a map of it on the fly.