Here's some video of this year's trials of The Fountain of Fizz: the Mentos-Diet Coke geyser.
The lesson we do at Rio Phyz does not involve nucleation sites or carbon dioxide. That's all good stuff, but it strikes me as the Chemistry in the Fountain of Fizz.
The Physics of the Fountain of Fizz involves measuring the mass ejected, the height attained by the geyser, and the time of the eruption.
With these quantities in hand, it's possible to make reasonable calculations of mass flow rate, muzzle speed, energy released, and power developed.
Physics in the Fountain of Fizz (PDF)
This lab is also included in my lab manuals for the following Pearson titles:
Conceptual Physics 11/e (College) [Hewitt/Baird lab manual]
Conceptual Physical Science 5/e
Conceptual Physical Science—Explorations 2/e
Conceptual Integrated Science 2/e [available early 2013]
Conceptual Integrated Science—Explorations
But if you're into carbon dioxide and nucleation, have at it!