Firefly is a great demo of the energy harvesting property of piezo PVDF film. With 730 pF capacitance and 57mm x 15 mm active area, the piezo PVDF film can convert mechanical vibration to >100 V output and ignite a neon bulb (though current output is low). The electrode is screen printed silver ink.
It can also be used as a vibration sensor.
Made with PolyK piezo PVDF film with high d31. The 120 um thick piezo film with silver electrode is a good material for energy harvesting due to its mechanical robustness and high output voltage: http://piezopvdf.com/pvdf-piezoelectric-film-120-um-thick-silver-ink/
Other sensor size can be produced upon request.
Youtube video on firefly: http://youtu.be/50nsz4Z6U1Y
You can also make your own energy harvesting "shoe" sole by following this procedure:
This can convert your walking to electrical energy and charge your smart phone or smart water.