jQuery ClassyNotty is a plugin that enables your application to display unobtrusive, beautiful and elegant notifications.
jBar is a simple and lightweight jQuery notification banner which is an alternative to the Hellobar. It allows you to create a simple call to action and bring it forward for the user to see at the top of your website. The user can then toggle the visibility of the bar by clicking the ribbon.
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
noty is a jQuery plugin that makes it easy to create alert, success, error and confirmation messages as an alternative the standard alert dialog. The notifications can be positioned at the top, topCenter (like GMail), bottom, centre, top left or top right. There are lots of other options in the API to customise the text, animation, speed, buttons and much more.