Have you ever seen a lightbox or greybox effect with ajax. If don’t, open Reviewme.com and then click login. It will trigger open new small window to login, appear with some light effect most color effect is from default background to gray or white. That called Ajax LightBox or Ajax GreyBox.If you want to learn more how to install on your websites/blogs. Here are resources the list:

Orangoo Labs - GreyBox can be used to display websites, images and other content in a beautiful Showing external pages; AJAX uploading of files; Showing internal pages

YUI Based Lightbox - YUI Based Lightbox in Cool AJAX sites - a YUI based image gallery script.

GreyBox 5 - Actually, GreyBox 5 is almost a framework for creating kick-ass pop-ups …

Lightview - Lightview was built to change the way you overlay content on a website. We have to use Prototype 1.6.0.2 and Scriptaculous 1.8.1

Multibox - Only use Mootools JS Library. Very cool

LightWindow - Required Prototype + Scriptaculous (165k). Supports EVERY Media type and renders it appropriatly.

Lightview for WordPress - Lightview is similar to Lightbox yet superior to Lightbox. Since version 2.0, Lightview has been able to overlay not only images but also videos

MOOdalBox - A modal box (inline popup), used to display remote content loaded using AJAX, web 2.0 style, written for the mootools framework.

iBox - lightweight script that lets you overlay images and documents in a small dialog without a page reload. It’s built to be easy to install and use

Facebox - a jQuery-based, Facebook-style lightbox which can display images, divs, or entire remote pages. It’s simple to use and easy on the eyes.

I only mention 10 of the list, actually still many others you can googling it. And every single list have their own pros and cons, specially on size of Javascript library. GreyBox and Ajax LightBox very useful when you create small web apps to display images, web form, external page, or video/movie.