I wouldn't suggest trying this one inside, but you can achieve some pretty remarkable results when you quickly drop a dozen Mentos into a 2-liter bottle of Diet Coke.
How high did the soda erupt? Judging from the slow motion that we replayed in master control, it looks like the soda shot up to about 16 feet. That's the power of carbon dioxide in a 2-liter bottle of Diet Coke. And yes, Diet Coke remains to be the best performer (and I've tried almost everything).
More details and way cool video
here.