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.

sammychen

This plugin will automatic add links to technorati tags or your blog’s tags where the words in your post match the tags of that post.
The most greatest things is that the plugin will not actually change your posts’ content in order to add links, so it will not hurt your posts. If you don’t want to use this plugin, just deactive it, and all links the plugin generated will automatic disapper just like they automatic come out, then your blog will return to its original status.
Go to Settings->Tag to Link for more information.
Rules Of Match 
Here are some rules when and how the convert take actions. These rules are only effective after version 0.5
<ol>
<li>If you tagged a post ‘hello world’ ‘hello’ ‘world’ and the content of your post is ‘hello world, I’m coming’, then this plugin will add link to ‘hello’, ‘world’, but not ‘hello world’, because there are links already. The rule can be simplily called Short Tag First.</li>
<li>If you tagged a post ‘hello world’ ‘hello’ ‘world’ and the content of your post is ‘bigworld, hellod, world’, then this plugin will add link to the last ‘world’, and no links will be added to ‘world’ of ‘bigworld’, or ‘hello’ of ‘hellod’.</li>
</ol>

Automatic Tag Link

This plugin will automatic add tag links to words in your content match the tag.

TagGator vs Automatic Tag Link