This is one of those instances where you have to click through to the Spritely site to have any idea what I'm talking about.
See those birds that look like they're flying? It's because they really are. And you can click anywhere on the site to move them. It's strictly HTML and jQuery, so no issues with Flash. If you have no idea what that means, that's okay....just know that it's really simple to download for your own site, and if you want to know all the details, it'll explain them.
Otherwise, go have 20 seconds of fun, playing with those birds. Drag and drop them, watch the background, click a random spot anywhere on the page, whatever. Oh, and if you do nothing else, drag the little slider at the bottom of the banner to see them go super fast in either direction. It makes me giggle, hehe.