So by now we all know that if you add Mentos to a two-liter bottle of Diet Coke you get a soda geyser, something like this (details here). Videos of this phenomenon abound on the 'Net and even David Letterman has gotten into the act, but these guys (seen at the end of the Letterman video: EepyBird.com--"Entertainment for the Curious Mind") turn an otherwise interesting effect into an art form. Check out The Diet Coke and Mentos Experiments and The Diet Coke and Mentos Experiments II and prepare for inspiration.
Uh, not that I would ever incite anyone into performance art for my own amusement or anything, but, for informational purposes only (heh heh!), one might investigate Steve Spengler Science's Geyser Tube and ponder its possibilities (as they do at GeyserTube.com).
By the way, I notice from the videos that Diet Coke seems to outperform Diet Pepsi in terms of geyser height and, as a side note, Jamie Hyneman of MythBusters says "Mentos, which is all well and good, and it works quite well, is actually not the best performer in creating this eruption. Plain old table salt is better." This needs to be tested and performed as a Do Something Different Day activity.
Incidentally, soda geyser experiments are way safer than making a glowing pickle ( and this link for more) and certainly less hazardous to your household appliances than generating microwave grape plasma.