Earlier I had written about LightBox a JavaScript application which "is a simple, unobtrusive script used to overlay images on the current page. It's a snap to setup and works on all modern browsers".
Now Lokesh Dhakar has released a new version LightBox 2.0 which supports animations and cross fading, along with navigation as well. It's an amazing application and prime example of the power of JavaScript.
Rushi's Ramblings 
This script is amazing! Especially, the navigation part.