This inexpensive robot is built on Sparkfun's $15 Magician chassis and uses a variety of sensors to showcase the 20M2's many amazing features.
Three touch sensors, IR and ultrasonic ranging, and twin IR receivers allow lots of interaction.
ROBOT magazine covered the build in two print issues, Sept/Oct and Nov/Dec 2012. Construction details, schematics, photos, sources and code are on the companion web site at http://find.botmag.com/091206 and http://find.botmag.com/111207 .
Many videos are listed there, including a touch sensor demo: http://www.youtube.com/watch?v=3e92B8JNNns and an IR beacon tracking demo: http://www.youtube.com/watch?v=3rHuFFe6HRc