
The Ants are a community of cubic-inch microrobots at the MIT Artificial Intelligence Lab. There are two main goals for this project. The first is to push the limits of microrobotics by integrating many sensors and actuators into a small package. The second is to form a structured robotic community from the interactions of many simple individuals. The inspiration behind this idea comes from nature — the ant colony.
The Ants: A Community of Microrobots: [Link]

This AVR controlled autonomous robot is programmed to follow the brightest light in the room. It uses two wheels and a ping pong ball as a third wheel. Really simple components here and it runs on three AA batteries to sweeten the deal.
Robot follows the light with a ping pong ball: [Via] - [Link]

Snaky is built around a powerful ATMEGA88 AVR microcontroller from Atmel, twelve miniature servo-motors and a few other components. On the software side the most CPU intensive section is the PWM generation, as 12 PWM signals are generated with a resolution of 20μs and a quite high pulse refresh rate. To achieve this target an innovative firmware architecture is implemented, managing two PWM channels at a time.
Snake robot named Snaky: [Via] - [Download Project] - [View Project PDF]

The Sandwhich robot is a cool little robo(line follower robot) that is made from easy to find parts , not to mention cheap, and stuffed together into a plastic sandwich box.
Sandwich Robot (line follower robot): [Link]