Freeow! is a plugin for making Growl-like alerts or message boxes on your website. You can customize the look and animation of Freeow! each time a message box appears, and you can alter other options such as whether or not to have the message box hide itself automatically.
jQuery Ambiance allows you to create notifications on the fly by just calling the function and providing some information
Display text, html content, images and ajax requests with 5KB code.