Cell Size and Scale visualization from the University of Utah, the Scale of the Universe visualization from Cary and Michael Huang, and the Universcale from Nikon.
A new entrant in the field called ChronoZoom ups the ante. You have to see it for yourself. It's a really impressive visualization (HTML5) tool that explores Big History. The people behind the project have lofty ambitions for the future and they're looking for users:
ChronoZoom Beta is ready for mass consumption and feedback, structured to scale up to petabytes of content, and architected for the future of personal computing.