Sweets and Diet Coke

Here's a marketing coup that has exploded all over the internet. The
humble Mentos sweet has been found to have spectacular properties if
mixed with Diet Coke. Popping the sweet into a Diet Coke bottle
causes a reaction that results in a 20ft geyser shooting into the
air. Mentos has found about 800 videos of the soda fountains all over
the internet and estimates the free publicity to be worth 10m
dollars.

http://www.youtube.com/watch?v=YNgl6z5Z7k4&search=mento