All the Free jQuery Plugins about 'Ajax' are listed here.
prettyPhoto is a jQuery lightbox clone. Not only does it support images, it also support for videos, flash, YouTube, iframes and ajax. It’s a full blown media lightbox. It also comes with useful APIs so prettyPhoto can be launched from nearly anywhere.
TextExt is an autocomplete and tag input plugin for jQuery which allows you easily turn a standard HTML text input into a wide range of modern, tailored to your needs input field without bloating your source code and slowing down your site with the code that you aren’t using.