Mark Jaquith

This plugin increases the height of the category checklist meta box on the post editing screen so that all categories are shown. No more scrolling! All of your categories will be visible. If you’ve been frustrated by having to scroll to find the correct category, this plugin is for you. No options. Just install it and you’re good.

Category Checklist Expander

Increases the height of the category checklist meta box on the post editing screen so that all categories are shown.

Ben Huson

<blockquote>
This plugin in only required for versions prior to WordPress 3.5 
 I am no longer continuing to provide support for this plugin. If anyone would like to take over commit access please contact me via the details in my profile.
</blockquote>
This plugin collapses and reduces the height of hierarchical category and taxonomy panels in the WordPress admin.
It always bugged me that when editing a post the categories panel took up so much height if you only had a few categories. This was also the same for custom hierarchical taxonomies.
This plugin just adds a couple of styles to your admin to override this and collapse that space.
I created an initial patch for this which, with contributions from other WordPress developers, was included in WordPress 3.5. You can <a href="https://core.trac.wordpress.org/ticket/15925" rel="nofollow ugc">see the patch here…</a>

Compact Taxonomy Checkboxes

Collapse and reduce the height of hierarchical category and taxonomy panels in the WordPress admin (not needed for WordPress 3.5+).

Category Checklist Expander vs Compact Taxonomy Checkboxes