InnerFade
InnerFade is a small plugin for the jQuery JavaScript library. It’s designed to fade you any element inside a container in and out.
Demos and download: http://medienfreunde.com/lab/innerfade/
BlockUI
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.
Its flexibility is especially useful when mixing it with ASP.NET. For example, see my recent examples of using it to provide progress indication during a partial postback and displaying a modal confirmation dialog after an UpdatePanel refresh.
Demos and download: http://www.malsup.com/jquery/block/