Haris Zulfiqar

WordPress tooltip plugins lets you add tooltips to plain text and links on your post and pages.
It offers a tinyMCE shortcode GUI which will guide you through the entire process of a tooltip.
This plugin uses jQuery tipTip authored by Drew Wilson http://code.drewwilson.com/entry/tiptip-jquery-plugin.
You can also add tooltips manually by following the pattern below:
<pre><code>[tooltip content="This will show in a tooltip" url="This will make tooltip a link"]Hover over me for tooltip[/tooltip]
</code></pre>
Url is optional. If URL is added, it will render a link otherwise it will be a plain text.

WordPress Tooltip

WordPress tooltip lets you add tooltips to content on your posts and pages.

eduardosada

WP-TagTip is an sexy way to show a related post of one specific tag with tooltips.
Please visit <a href="http://www.coders.me/wordpress/wp-tagtip" title="WP-TagTip" rel="nofollow ugc">the official website</a> for further details and the latest information on this plugin.
<h4>Licence</h4>
This plugins is released under the MIT, you can use it free of charge on your personal or commercial blog.

WP-TagTip

An sexy way to show a related post of one specific tag.

WordPress Tooltip vs WP-TagTip