Small, easy to use and maybe just what you are looking for: This jQuery plugin provides you with customizable tooltips.
As soon as the jQuery SVN repository is available again, I’ll commit the source, so anyone can improve the implementation if he likes.
Comments are welcome!
The Tooltip plugin is now update. Thanks to Andy Matthews for some great ideas. The Tooltip can now be styled with transparent PNG backgrounds, the plugin handles the necessary fix for IE. It also supports a little text parsing to generate header and body texts, switching URLs on and off, and, last but not least, global settings.
In addition, you can now find the source in the plugin repository, making it easier to update it.