this is definitely in the running for that illustrious and ever-changing title. "The Scale of the Universe 2" is an interactive Flash activity with a slider that goes from a scale of 10**(-35) meters (ten to the minus thirty-fifth power, very small) to 10**27 meters (bigger than the known universe).
Cary Huang. It's similar to the famous "powers of ten" movie except you can control it in both scale and speed (about 13 seconds to go from smallest to largest at maximum scroll rate) and you can click on objects to learn more about them. It comes complete with spacy background music. Awesome! Thanks to Matt Bors for posting this on Facebook.