“Youtube ToolTip” is a simple plugin, which changes all your links of “youtube” on a fast preview for the convenience of your readers.
Modifying all the links and using “jQuery” shows an attractive & modern blog.
Also use “qTip”, qTip is a tooltip plugin for the jQuery framework. It’s cross-browser, customizable and packed full of features! 
qTip is licensed under the open source MIT license, which allows you to use the script for whatever you want, whenever you want, however you want, as long as you include a copy of the license!
For more information about this plugin visit http://javiergalicia.wordpress.com/2009/07/03/youtube-tooltip-to-wordpress/

Youtube ToolTip

"Youtube ToolTip" Click on any of your links to get a quick preview of the youtube video.

Jesper Johansen (jayjdk)

This plugin, Jayj Quicktag, allows you easily to add custom Quicktags to the post, page, or a custom editor.
It adds a settings page where you can add all the Quicktags you want (see Screenshots)
It supports both import and export of your Quicktags so you easily can add them to another WordPress install.

Jayj Quicktag

Allows you easily to add custom Quicktags to the post editor.

Youtube ToolTip vs Jayj Quicktag