CNN’s The Moment combines hundreds of user-submitted images of the Inauguration into one 3d scene. It’s navigable (although rotating may induce brainfuzz) and you can zoom into specific pictures. Pretty impressive: it uses Microsoft’s Photosynth technology, which I really must have a proper play with. Requires Silverlight.
Update: Metafilter has links to satellite images of the inauguration crowds. Humanity = ants.