There are times that you need to know the ID number of a page or post in WordPress and it can be more painful than it should be to find that number. This plugin does one simple thing: it displays the ID number of the page, post, category, or tag you are looking at in the WordPress Admin Bar. It appends this ID to the edit menu already on the Admin Bar. Needless to say, that means that this plugin is only useful for WordPress version 3.1 or above, since the Admin Bar was first introduced with 3.1.

Admin Bar ID Menu

Makes the ID number of the current page or post visible in the Admin Bar.

harman79

This plugin is all about IDs and offers a twofold functionality.
a) Adds a custom admin options page with WP List Tables that allow you to get a delimited list of post/page IDs by taxonomy / tag or post type. Listing of IDs by template only works for pages, not posts.
This can be particularly useful when for example you are working with WP conditional tags, where it is common practice to create a delimited list of post or taxonomy IDs. If there are many posts or taxonomies required, the process of finding each ID one by one can get a bit annoying and time consuming.
This plugin makes it easier for you. It creates delimited lists of post/page IDs based on taxonomy/tag, post type, template or user selection from WP list-tables.
b) Adds a column displaying IDs in the posts/pages, media, taxonomies and users screens. It also offers the option to automatically copy the IDs of selected items.
For a clearer picture please have a look in the Screenshots section.
Features:
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Works for built in and custom post types and taxonomies.
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Works fine with Woocommerce and WPML.
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Provides a settings page to control functionality.
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An auto-copy to clipboard function is also provided.
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Note: The “Copy Selected IDs” button added in the WP built-in post/page and taxonomy list edit screens uses Javascript and works for all major browsers (Note: IE 10+). The auto copy to clipboard function is not supported by Safari, but you still get the selected IDs in the textbox, so you can copy them manually.

ID Arrays

Get list of post IDs by taxonomy, post-type, template. Add ID column in posts, media, taxonomies, users screens with option to copy selected IDs.

Admin Bar ID Menu vs ID Arrays