In a modern variant on the Powers of Ten video, Cary and Michael Huang have created an excellent flash game that spans the scale of the universe, from the smallest, only hypothesized particles, through atomic, human, planetary, and galactic scales (to name a but a few), to the size of the universe itself. It goes further than the Cell Size and Scale flash app.
The link is here, but look out for an advertisement that takes up the game window, which will eventually let you through (or you can click the “Skip Ad” link on the bottom right of the ad).
Check out this similar app with real pictures: http://cosmicscale.appspot.com/