At the exhibition of the Dutch Electronic Art Festival 2007 in Rotterdam, one interesting piece was 'Ondulation', by Thomas McIntosh. A "composition for water, sound and light," it could also be described as a lesson in wave theory. A large pool of water is set in motion by sound, and the wave patterns are reflected onto a screen. The result is mesmerizing. (Though, paradoxically, the tranquil quality of the wave patterns is somewhat lessened by the droning sound.)
More images and video here.