PicLens is a browser addon for Firefox, Internet Explorer or Safari which lets you view images from a number of popular sites including Flickr and Google Images, in a full screen, 3D environment.
Apart from being a pretty way to browse images, it's also practical - it lets you view large number of images very quickly.
The way it works is when you're on a page which supports PicLens (and it's a lot of the major ones, including Google Images and Picasa, Flickr, Facebook, MySpace and Deviant Art) or any site which supports Media RSS, you can mouse over any image and click the PicLens button that appears. This will bring up a 3D gallery called "The Wall" which stretches into the distance. You can rapidly scroll through it, then click on an image to see it in full size.
I get the feeling my description is not doing it justice, and I know the screenshot doesn't do it justice (hit the jump to see it). Check out the demo video to get a feel for just how beautiful it looks and how beautifully it navigates.