[Greg Marra]

I got this kit once that was a bunch of thin wooden dowels and a bunch of glow-in-the-dark 1cm wide rubber rings. You pushed the dowel through the edge of the ring and could build little structures out of it. I made a pyramid that still hangs from the ceiling of my room over 6 years later.

I don't know if there's a "World of Science" store near you, but we used to have one in our mall and it was full of really neat things that could get kids interested in science.

How about magnets? I always loved magnets as a kid. Get two ring magnets and a pencil and you have an anti-gravity device!