In light of recent events in Japan, or just in the course or your curriculum, you may be looking for ways to help your students understand nuclear energy.
I just stumbled across this publication, Nuclear Experiments You Can Do, from the Charles Edison Fund..
The pdf file includes simple models/demonstrations for splitting an atom and chain reactions, as well as more
advanced demonstrations related to nuclear energy and radioactivity.
I wanted to pass this your way as quickly as possible, since it is a timely topic. As a result, I haven't looked through the other experiments available, but they could very well be worth taking a look at.