WP Best Tree – WordPress Plugin
This plugin improve usability for categories meta boxes on the post editing screen.
See the official plugin page or see video preview on YouTube.
Toggle style for child categories and taxonomies
In WordPress, after a post is published, the selected categories are no longer displayed in a hierarchical and climb to the top of the list. This plugin maintains the hierarchy of categories even after the post was published.
Good Quality Code (jQuery Enhanced & Simple CSS)