jGrowl
jGrowl is a jQuery plugin that raises unobtrusive messages within the browser, similar to the way that OS X's Growl Framework works.
Beginning with the 1.0.2 release I've included a demo file and a stylesheet to accompany the release.
Example Usage:
$.jGrowl("Hello world!");
$.jGrowl("Stick this!", { sticky: true });
$.jGrowl("A message with a header", { header: 'Important' });