This plugin shows post/page/category/tag/comment IDs on admin’s edit post/page/category/tag/comment pages. You can see the ID when you visit an edit post/page/category/tag/comment page and put the mouse pointer on.
This plugin hooks on ‘edit’ link and privileged user can see IDs. For example, a user of author role can see post IDs, but a user of subscriber role can not.
Requires WordPress Version: 2.9 or higher