The SkinnyTip tooltip library is under 10kb in size, and supports the latest versions of IE, Firefox, and Netscape. View browser compatibility chart.
SkinnyTip is also available as a Wordpress plugin, which allows you to generate SkinnyTip Tooltips easily when you create a post in your Wordpress site.
Best of all, SkinnyTip is easy to install and configure. Very easy. And it is free!Examples(mouse over the links):
For help configuring and using SkinnyTip, check the easy setup instructions in the Documentation section.