Chladni Plates are flat vibrating metal plates which, when sprinkled with salt, show very interesting patterns. If the salt is replaced with a liquid, you can get 3D patterns.
You can see this for yourself if you take a polystyrene cup of black coffee and move it slowly across a flat surface (you may need to apply slight pressure). The cup vibrates, and the vibrations are passed onto the liquid, appearing at the surface as a series of quite pretty standing waves.
I've also seen similar patterns at the event Seven Eighths Of A Second, which used real sounds rather than standardised tones to drive the process.