Following lines, detecting colors, responding to light. It is still far from "seeing", but the LEGO Mindstorms EV3 & NXT sensors could be very useful when used properly.
Building instructions for a Robot Grabber used in the World Robotics Olympiad competition runs. The grabber is build with LEGO Mindstorms EV3. The base of the robot is available at /materials/69-wro-robot-2014-elementary
Building instructions for a robot for the World Robotics Olympiad Sputnik competition. This is the light version without the lift at the top.
Building instructions for the LEGO Mindstorms EV3 robot used for accomplishing WRO 2014 mission. It is the full robot with the lift at the top