We own a children's science education company, and we do TONS of stuff with dry ice. The kids just LOVE IT!
Take a quarter and hold the block of dry ice in your hand (with gloves obviously) push the quarter into the ice, so it "cuts" a line in it... then place the quarter in that slot that the quarter carved. The quarter will begin to "shiver" you can explain the science behind it... that the quarter is on average 180 degrees warmer than the ice, so it's heat is forcing sublimation (the release of the gas) so that gas release is what is moving the quarter.
You can also make a spoon scream, when pressed against it.
You can take a bowl of water and add some dish soap then drop the dry ice in (if you break it up, it will sublimate faster and will give a bigger "wow") and it will make HUGE bubbles over the bowl.
We have a "shower" we constructed that we have a long tube, and a curved top that we dip in bubble solution... so we make gas filled bubbles that are awesome, but that one can't really be duplicated at home without the contraption.
I love dry ice