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.

Kharis Sulistiyono

Dropdown hierarchical category in WordPress post write panel or editing screen. It makes the categories or taxonomies list in a better UI which enables show/hide toggle of child categories. It comes with plugin settings page where you can select in what custom post type(s) the dropdown UI will be applied to.
The idea comes from default WordPress hierarchial post categories which looks not good. Imagine that there are a lot of child categories. After selecting child category then publishing or updating a post, the arrangement seems not pretty — the child categories moved away from its parent. This plugin tackles that situation.

WP Dropdown Hierarchical Category UI

It makes the categories or taxonomies list in a better UI which enables show/hide toggle of child categories. Supports any custom post types.

Category Checklist Expander vs WP Dropdown Hierarchical Category UI