Mark Jaquith

<ol>
<li>Check a category.</li>
<li>Uncheck “Uncategorized”.</li>
<li>Mutter “stupid ‘Uncategorized'” under your breath.</li>
</ol>
Sound familiar? With this stupidly simple plugin, you just have to do the first step. When you check a category and the default category was the only thing checked before you clicked, it’ll uncheck the default category for you. Boom.

Categorized

Unchecks the default post category when you first select a non-default category

scribu

This plugin is outdated. Use <a href="https://wordpress.org/extend/plugins/term-management-tools/" rel="ugc">Term Management Tools</a> instead.

Merge Tags

Adds a new form on the tag management screen that lets you merge and replace tags and categories.

Categorized vs Merge Tags