水野史土

This plugin shows post/page/category/tag/comment/media/user IDs on admin’s edit post/page/category/tag/comment/media/user pages. You can see the ID when you visit an edit post/page/category/tag/comment/media/user page. 
Since this plugin hooks on ‘edit’ link, only users with priviledges can see IDs. For example, a user of author role can see post IDs, while a user of subscriber role cannot.
You can find a brief description in Japanese on a book <a href="https://php4wordpress.calculator.jp/" rel="nofollow ugc">Introduction to PHP for WordPress Users.</a> (written in Japanese.)

ShowID for Post/Page/Category/Tag/Comment

This plugin shows post/page/category/tag/comment/media/user IDs on admin's edit post/page/category/tag/comment/media/user pages.

nickohrn

gambit37

This plugin restores the link, post, and page Id columns to their respective management interfaces. This plugin could be used by designers when making complex themes that require knowledge of specific link, post, or page Ids.

Restore Post Id

This plugin restores the link, post, and page Id columns to their respective management interfaces.

ShowID for Post/Page/Category/Tag/Comment vs Restore Post Id