OddWires’ obstacle-avoiding robot kit is a cost-effective learning platform for robotics. It chassis rolls on two wheels and a castor, to simplify programming for beginners. The kit includes two geared DC motors, an Arduino Uno R3, motor shield, a servo, ultrasonic sensor, a 6V battery case with 2.1mm plug for Arduino, and a small bredboard. A sample sketch to drive the robot, too.
You can buy the kit on the OddWires Website for $79.95.