Here is another kit that lets you build your own cool robot with Arduino. The OSEPP Robotic Functional Kit comes with an ultrasonic sensor for object avoidance and IR follower module. The kit contains an OSEPP UNO R3 PLUS micro controller board, TB6612 Motor Shield and sensors to help you get started.
With the Bluetooth module, you can control your robot from your Android device. The assembly instructions and code are open source.