Fabio M. Giacomini

This plugin adds a new field in every post, where you can write a text that will be inserted in the related meta tag, located in the head section.
The main options page of the plugin, provides you with a default text area, where you can insert a default description that will appear in case the field in post page is empty.

Single Post Meta Description

The easiest way to add in every post page a different meta description tag, located in html head.

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.

Single Post Meta Description vs WP Simple SEO Meta