PSMAN

TagGator is an auto tagging plugin, Just write enter a few keywords representing your contents, TagGator will automatically scan your posts for these keywords, and tag them according to the results.
A Pro Version of TagGator is now available with the following features:
<ul>
<li>Auto Tagging: Your posts are tagged automatically when you create posts.</li>
<li>Autoblog friendly:Taggator works with most autoblogging solutions, tags are created automatically when the posts are generated.</li>
<li>Keywords To tags: Just write different keywords that represent you tags, Taggator will create the tags, and assign them.</li>
<li>Set & Forget: You only need to configure TagGator once. once done, you won’t have to worry about tags anymore</li>
</ul>
<a href="http://codecanyon.net/item/taggator-pro-wordpress-auto-tagging-plugin/1725033?ref=AngryByte" rel="nofollow ugc">Click here to learn more & get TagGator Pro</a>

TagGator

TagGator Automatically tag to your posts so you dont have to! Tag your posts based on their contents automatically.

techphernalia

This plugin helps your SEO by adding meta keywords tag to each page, post, archive (category, tag, date, day and year). 
Now it also allows you to specify common keywords to be included on every web page. Plugin from one of the best coder <a href="https://www.techphernalia.com/" rel="nofollow ugc">Durgesh Chaudhary</a>. 
For any support just leave your question at our <a href="https://www.techphernalia.com/meta-keywords-generator/" rel="nofollow ugc">Meta Keywords Generator</a> page.
Uses Title, Description, Categories, tags, Compulsary keywords (provided by you in setting) for keywords generation. Uses content after striping short codes and short tags for generation of description.
Reduces manual work of adding them manually.
Now more efficient by allowing you to add one time master keyword list.
A big Thanks to Omer Barlas for suggesting to change text box to textarea for better readability.

Meta Keywords Generator

Adds Meta keywords and Description to each and every page, post, archive.

TagGator vs Meta Keywords Generator