A Van de Graaff generator with paper streamers taped to the dome shows the radial shape of the electric field produced by the generator. Can also show the distortion of the field due to the introduction of a grounded metal rod. This works much more reliably than getting hair to stand up.
Use either the round or pointed end of the discharge wand to show their effects on the electric field.
Note: Be sure the discharge wand is physically touching the dome before turning it off.