Kilobots made by the Self-Organizing Systems Research Group
Kilobots are quarter-sized robots that move on three little legs designed to interact and coordinate their behavior. Created by the Self-Organizing Systems Research Group at the Harvard School of Engineering and Applied Sciences (SEAS) these little robots can be used to experiment with swarming algorithms. They have recently teamed up with the K-Team Corporation, a Swiss manufacturer of high-quality mobile robots, to mass produce kilobots so that researchers and enthusiasts alike can experiment with their own robot swarms.
More information can be found at Science Daily.
Their research group has some amazing videos of quadrotors in coordinated flight, and quadrotors working together to perform a coordinated construction task. The GRASP lab is involved in numerous other projects that are worth checking out.
Here is a video of quadrotors in coordinated flight: