Overlay

jQuery ContentHover Plugin is a small jQuery plugin that helps you show some hidden content on top of an element when the mouse hovers over it. There are options to choose how your hover effect would appear, like fade in or slide in from any direction, you can change the opacity of the overlay etc.  

The jQuery BlockUI Plugin lets you simulate synchronous behavior when using AJAX, without locking the browser. When activated, it will prevent user activity with the page (or part of the page) until it is deactivated. BlockUI adds elements to the DOM to give it both the appearance and behavior of blocking user interaction.  

Chardin.js is a jQuery plugin that creates a simple overlay to display instructions on existent elements.  

isLoading is a simple jQuery plugin to show visual feedback when loading data or any action that would take time.  

Hover Captions is a jQuery plugin that enables you to display caption overlays with cool effects over images, div's, ect..