thunderbax

The plugin add a custom page in your admin dashboard where you can show html code to editors. 
You can edit the html text directly in a box place in option page with a WYSIWYG editor. 
All html, javascript, css are supported. 
You can also insert Youtube videos or images.
Related Links:
<ul>
<li><a href="http://www.thunderbax.com/?page_id=767" title="WP Admin Custom Page Plugin for WordPress" rel="nofollow ugc">Plugin Homepage</a></li>
<li><a href="http://www.thunderbax.com" title="Author Homepage" rel="nofollow ugc">Author Homepage</a></li>
</ul>

WP Admin Custom Page

The plugin add a custom page in your admin dashboard where you can show html code to editors.

Arno Esterhuizen

When you add text to the category description textarea and save the category, WordPress runs content filters that strips out all but the most basic formatting tags.
This plugin disables those filters for roles with the necessary permissions. Any html code you add to the category description will not be stripped out.
This plugin does not do anything other than disable the filters. It does not protect you from entering invalid HTML, nor does it help you create WYSIWYG HTML. You can use the post or page composing screen to help you create the text and formatting. Switch to the ‘code’ tab and copy the HTML code into the category description field.

Allow HTML in Category Descriptions

Great Plugin

This plugin allows you to use unfiltered HTML in your category descriptions by disabling selected WordPress filters.

WP Admin Custom Page vs Allow HTML in Category Descriptions