No strictly space related but pretty cool. Researchers at Carnegie Mellon created a multi layer display using a single projector synced to water droplets. The multiple plane Tetris game is interesting.
When giving talks the current count of exoplanets comes up sometimes. I encourage the kids to look frequently at
http://planetquest.jpl.nasa.gov/ its still at 453 today.
Science Mission Directorate Space Science Education has a nice Resource Directory which makes it easy to find activities and other resources by subject area and or grade level. The space math activity which uses LRO images of the Apollo 11 descent stage for teaching measurement techniques is particularly cool.