Dynamic Widget is a plugin for JQuery UI that automates lazy loading JS and CSS for your JQuery UI widgets without the need to worry about includes.
jQuery Ajax Loading.
A jQuery plugin that provides callbacks for images, letting you know when they’ve loaded.
Easy jQuery plugin to show visual feedback when loading data or any action that would take time. Also can disable form elements and put an overlay an specified area or whole page.
Multi-functional image preloader plugin for jQuery
With this plugin, you can display a loading overlay on any bloc