Epigrade

Add page title, meta description, keywords and robots to all post types and taxonomies. 
Plugin will automatically change page titles for posts, pages, custom posts, categories, tags and custom taxonomies to 
whatever you have entered. Also will inject meta fields in template head section. If however you leave fields empty 
default WordPress or theme behaviour will occur. 
This plugin also removes taxonomy description column from listing table.
You can use it in your theme or other plugin. It creates the following taxonomy and post meta fields: 
 _page_title, <code>_meta_description</code>, <code>_meta_keywords</code>, <code>_meta_robots</code>.
Example usage:
<pre><code>// Get page title value for taxonomy with ID $term_id:
$taxonomy_title = get_term_meta( $term_id, '_page_title', true );

// Get page title value for post with ID $post->ID:
$post_title = get_post_meta( $post->ID, '_page_title', true );
</code></pre>

WP Simple SEO Meta

Add page title, meta description, keywords and robots to all post types and taxonomies.

pluginsforall

An easy way to add meta keywords to your posts and pages. Just put the keywords in the text field of each post or page and they will appear when the post or page is displayed.
<h3>Keyword Research</h3>
<a href="https://localruler.com" rel="nofollow ugc">Get keywords at localruler.com</a>

Local Ruler Meta Keywords Manager

An easy way to add meta keywords to your posts and pages.

WP Simple SEO Meta vs Local Ruler Meta Keywords Manager