The Most Beautiful Experiments in Physics

TheMatt writes "In this month's 'Physics World', Robert P. Crease asks the question: what is the most beautiful experiment in physics? Some criteria quoted are that it must change what people thought, must not be too complicated or expensive, and, most importantly, be within the reach of students (which leaves out Stern-Gerlach or Michelson-Morley). He also has a page at BNL reprinting the article, with a place for suggestions from the community on their opinion." I'll nominate a simple one: Foucault's Pendulum. :)