I happened to stumble on an interesting set of images comparing the sizes of the inner planets, then all the planets, then the planets with the Sun, then the Sun with other stars (including super-massive Antares). The images are sort of 3D (almost like photos of models), but the JPG's are so compressed and faded that it's hard to tell. Still extremely cool and humbling - the Sun is but one pixel (and the planets invisible) in this final image where Antares is the big guy (about 370 pixels). This page kicked around a lot of blogs over the last few months and many people wondered from the poor quality if there wasn't a better original source somewhere, but I couldn't find one.
But I did find this Java applet that offers an interactive powers-of-ten zoom from 10**+23 meters (ten to the twenty-third power, or 10 million light years, multiple galaxies in view) down to 10**-16 (one femtometer, the scale of quarks inside a neutron) in 39 order-of-magnitude steps. Also very cool (use of the applet requires that you install/enable Java in your browser, and don't even think about posting an image from the site) .
(The Java applet is from Molecular Expressions, a wonderful site I have visited many times for their optics and microscopy related Java applets, but I never saw the Powers of Ten one before.)