The Pololu 3pi+ 32U4 OLED robot is a complete, high-performance mobile platform based on the Arduino-compatible ATmega32U4 MCU. Its many features include dual quadrature encoders for closed-loop speed or position control, line sensors, front bump sensors, a full IMU (3-axis accelerometer, magnetometer, and gyro), and a graphical OLED display, all packed into a robot that fits in the palm of your hand. This Standard Edition version is assembled with 30:1 MP 6V Micro Metal Gearmotors, which offer a good combination of speed and controllability.
More information is availibe at Pololu.