Similar to this question: what experiements do you think are impressive for layman adults?
I for example like how you can simulate an Einstein Ring with the bottom of a wine glass.
it depends on the how much structure/money you have to "invest". I always find a unvaluable amount of ideas watching the lessons of W. Lewin from MIT.
for each lesson he present a very scenographic but simple experiment to prove with some evidence the theory..
My personal favorite il the pendulum used to prove the conservation of energy! very entertaining!
Well known is the publication of 1890-1893 La Science Amusante par Tom Tit, 100 magical experiments to set up "science in play" in your living room, by Arthur Good. There are many modern variants in this tradition of amazing science experiments.
Experiments designed for children probalby are impressive for layman adults too!