I also have a recommended purchase from American Science and Surplus. I
have purchased their "Human-Powered Light" (#89928 @ $3.25 each) for
static electricity demos. When the students hold one of the two leads
and approach the Van de Graaf generator, the lights will glow. Also, we
use them to convincingly illustrate the difference between a conductor
and an insulator. If the kids rub a balloon in their hair and use the
light to pick up the electrons from the balloon, it is clear that they
must pick them up in clumps---ie that you cannot "ground" an insulator,
that even the extra electrons are tightly bound. Then, they charge an
electroscope and make contact with one lead to the electroscope, and
they get a brighter, one-time flash of light. I do not know if you can
get a similar type of light anywhere else. The kids really enjoy the
demos.