DanCoulter

Forgot the Category stops you from forgetting to set a category for a post. It simply pops up a Javascript alert box if 
you haven’t selected any categories when you save a post. That’s all there is to it.

Forgot the Category

Hate forgetting to select a category when you write a new post? I know I do.  This plugin won't let you.

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.

Forgot the Category vs Allow HTML in Category Descriptions