Steve

This plugin uses custom fields to allow the page title tag to be customised and differ from the actual page title.
Both meta descriptions and keywords can also be added if required.
Page meta details can be modified on any publicly accessible post type, such as posts and pages, as well as custom post types.
Theme and plugin developers should note that it is possible override the page title within your templates by setting <code>$wppm_title = 'Newly defined title';</code> before the call to <code>get_header();</code>.

Page Meta

Adds the ability to override the page meta title and add in meta descriptions and keywords for pages.

jim912

Outputs meta description and meta keywords in the element head. 
Notice! Current version japanese only, yet.
<h3>Links</h3>
“<a href="https://wordpress.org/extend/plugins/ps-auto-sitemap/" title="WordPress sitemap plugin">PS Auto Sitemap</a>” is a plugin automatically generates a site map page from your WordPress site. 
It is easy to install for beginners and easy to customize for experts. 
It can change the settings of the display of the lists from administration page, several neat CSS skins for the site map tree are prepared.
“<a href="https://wordpress.org/extend/plugins/ps-disable-auto-formatting/" title="WordPress formatting plugin">PS Disable Auto Formatting</a>” 
Stops the automatic forming and the HTML tag removal in the html mode of WordPress, and generates a natural paragraph and changing line.
“<a href="http://www.web-strategy.jp/" title="CMS service with WordPress" rel="nofollow ugc">CMS service with WordPress</a>” provides you service that uses WordPress as a CMS.

Meta Manager

Outputs meta description and meta keywords in the element head.

Page Meta vs Meta Manager