QRB1134 photoreflectors make great line sensors and can also be used with the IntelliBrain-Bot for wheel position encoding. These sensors attach to an analog input port but require a current limited circuit to power the emitter. The IntelliBrain controller provides an extra pin on four of its analog ports to power the emitter on these sensors.
Purchase a line sensor kit from the RidgeSoft store with two sensors and mounting hardware to mount them on the underside of your IntelliBrain-Bot.
The Devantech sonar range finders are great little sensors for sensing objects and measuring distances. The SRF04 provides a pulse output that can interface to the IntelliBrain, Handy Board or Sumo11 controllers. The SRF08 is more sophisticated and requires an I2C port, so it only works with the IntelliBrain.
The Nubotics WheelWatcher sensors are excellent quadrature shaft encoders designed specifically for use with hobby servo motors (WW-01) and Solarbotics gearhead motors (WW-02). These are great sensors for speed and position control, navigation, odometry, kinematics and stall detection applications.