PicLens: Cinematic Views for the Web
If you're on a Mac, check out PicLens - It needs OS X 10.4 and Safari 2, but most Mac users will have this.
Once it's installed (and Safari has been restarted) when looking over images on the supported web sites (like Google Images) you get a PicLens icon appear over an image when you hover the mouse over it.
Clicking on the PicLens icon then gives you a full-screen slideshow of the images on the page you're viewing... Pretty Cool!
