Teacher Slater Harrison has been teaching kids for years to fly gliders made out of low-density foam packaging. It's a magical thing to behold; it looks fake.
Each glider is like a paper airplane with potentially infinite flight—you push it along with air deflected off a pizza box lid (or your hands, if sufficiently advanced), flying the glider as long as you can keep providing lift. (Or at least until the slightest gust of wind comes along—these really don't work outdoors at all.)
The first time I saw one of these was in a clip from Going Deep With David Rees, on the "How to Make a Paper Airplane" episode. In that demo, a skilled practitioner was pushing it along simply using the air from his cupped hands.
Here's a demonstration of how to use pre-made gliders:
If you're into the whole DIY thing, here's an extremely thorough visual demonstration of the construction process (it involves shaving polystyrene):
Of course, Harrison has an extremely detailed site full of instructions on making your own, buying your own, working with classroom groups, and so on. Let's get flying, people!
(Via The Kid Should See This.)