I'm writing up a project for the forthcoming GeekMom
book that involves states of matter. Here's one I seem to have missed: Bose-Einstein Condensate. First created in 1995, it is not yet widely known or taught in schools. But an old page from website of the University of Colorado at Boulder actually does a pretty good job of explaining BEC
in words and animations simple enough for kids to understand.
And for all you educators out there, here's an interesting debate on the NSTA website
on if and when teachers should share the news that there are more states of matter out there than just solid, liquid and gas...