Mentos and Coke Fountains
If you missed Fritz and Stephen on Late Night with David Letterman or The Today Show, you can still see their "Fizz Fountain! Mentos and Diet Coke" video here. Totally cool.
For more fun videos on mentos and coke, just do a google search on the two words. A cautionary word, however, as I care too much for you all to let you go without one. You may not want to try the bombs as there have been many reports of broken noses and the like when they backfire and fly up into people's faces. I'd be concerned for innocent bystanders, too. Even for the fountains, I'd want to use protective goggles at the very least. (Being a geeky family, we've tons of them around.)