Using an oscilloscope to track waveforms is always interesting - but the effects of sound vibration on real-world materials can be downright stunning.
Try experimenting with different substances over a loud speaker, just don't spill any milk in your speaker cone!
Sound Waves on YouTube - Link
Snowy Day @ MGFest 2008 [via]-Link
Related:
Ruben's Tube - Sound visualization... with FIRE! -Link