Van de Graaf SnowStorm
This is one of the most spectacular Van de Graaf demonstrations, although it does require that you be on very good terms with your cleaning staff (and buy them the occasional present!)
Simple take a load of small pieces of paper - I mean absolutely hundreds of pieces by this! The small circular bits of paper from hole punchers are ideal for this purpose. Place them on top of the Van de Graaf, switch on and stand back!