I'm often asked to give quick demos of my robots to show off what they would be capable of in a classroom setting. I have three different models that I regularly fall back to to show off basic movement, the Ultrasonic Sensor, the Colour Sensor and the EV3's ability to play music. Description and Project file under the video.
1. Line follower. A simple line following robot using a single Colour Sensor in 'reflected light' mode. The program is a basic edge follower using a Switch statement inside a Loop
2. Obstacle Avoider. Using the Ultrasonic Sensor, this robot backs up when it gets close to an object. I put in an extra little 'back up and shake' routine as well as a sound effect to give it a little more personality.
3. Music Maker. This design only needs a Colour Sensor being used in 'Colour' mode. An extended Switch statement identifies which colour is under the sensor and then plays the appropriate note.
Demonstration EV3 Project file - demos.ev3
If you use any of these, please let me know how they go!