Automaton

Keepon, according to its creators, is:

...designed to interact with children by communicating attention and emotion. It has four degrees of freedom: attention is directed by turning +/-180° and nodding +/-40°, while emotion is expressed by rocking side-to-side +/-25° and bobbing up to 15mm. In addition to his role as a BeatBot, Keepon is used in research on social development and communication.

This little guy is capable of reacting to visual stimuli and of totally rocking out. The video below is both a neat demo of Keepon in public and an excellent music video in and of itself.

Another music video here, and a simpler video of Keepon in the lab reacting to objects here.