Mentos and Diet-Coke that creates such spectacular eruptions!
A 2006 Mythbusters episode had it partly figured out. Now students at Appalachian State University have filled in the details. The full story is over at ABC news, here. Make sure you check out the great clip from a world record set for 1360 simultaneous Coke-Mentos fountains.
Thanks to Rob at the Orbiting Frog for spotting this, here. Rob seems to have a soft spot for science experiments that involve food and drink as you can see here (Can crushing) and here (eating a microwave).