The chemical reaction featured on Monday Night’s Big Bang Theory, Season 3 Episode 9, “The Vengeance Formulation” (Nov 23, 2009) is known as Elephant’s Toothpaste.
It is done by combining hydrogen peroxide, dishwashing detergent, and saturated solution of potassium iodide. The experiment is detailed at this University of Minnesota Chemistry Department page.
Here is a video explaining the same chemical reaction:
update: it was removed; I will find another one some time.