With this plugin you can optimize your WordPress blog for search engines. 
It can automatically generate meta informations (like keywords and description for example) needed for the search engine optimization (SEO) of your blog.
The Keyword-Statistics-Plugin checks the content of a post or a page for keyword density (single words and optionally 2- and 3-word phrases; for each the 1-10 most commonly used can be displayed). 
It can update its informations automatically while the author is writing his content in a variable interval (every 1-10 seconds) or manually by clicking on a button. 
The script comes with english and german stopwords, which optionally can be filtered out before calculating the keyword densities. 
Moreover the commonest keywords are extracted in a list as a META keywords suggestion. 
Based on this list a META description can be created and automatically set. 
So the plugin can be used to do the on-page part of your SEO strategy.
Features:
<ul>
<li>Keyword density statistics about the usage of single keywords and keyphrases (2- and 3-words)</li>
<li>Setting an individual title for each page and post</li>
<li>META keywords will be set automatically based on the page content</li>
<li>META description generated from content based on the keyword statistics</li>
<li>Definition of individual titles, keywords and descriptions for all kinds of content aggregations. A set of variables that can be used on the specific aggregations – keywords will be filled up automatically to the maximum number of keys (you can define this too) with the ones generated from the listed posts.</li>
<li>Predecessors and successors that will be added to all page titles and descriptions served by your blog</li>
<li>Sitewide definition of meta keywords that will appear at the end or the beginning of the keyword list on each page of your blog – in addition to the ones defined for single posts or pages and at the various aggregations keyword lists.</li>
<li>Page-specific control of robots META</li>
<li>Generation of Canonical URLs – also for all kinds of content aggregation (lists with last posts, archive, tag, category, search results and author including pagination)</li>
<li>Controls the index/follow settings of the content aggregations (full control of robots for the specific aggregations)</li>
<li>Configuration of ODP, Yahoo! Directory and ARCHIVE (archiving of the content for search engines like google but also at archive.org) META</li>
<li>Prevents urls resulting in a not found response (404) from indexation</li>
<li>All meta tags generated by the plugin can be switched off separately to prevent collisions with other plugins</li>
<li>Using nonces for plugins security</li>
<li>Allow or deny indexation of the blogs feeds</li>
</ul>
Stopwords filtered for:
<ul>
<li>Brazilian Portoguese</li>
<li>Bulgarian</li>
<li>Czech</li>
<li>Danish</li>
<li>Dutch</li>
<li>English</li>
<li>French</li>
<li>German</li>
<li>Hungarian</li>
<li>Polish</li>
<li>Slovak</li>
<li>Spanish</li>
<li>Turkish</li>
</ul>
Backend translations for:
<ul>
<li>English</li>
<li>German</li>
<li>Slovak</li>
</ul>
Please notify: The SEO-relevant meta-information (meta keywords, meta description and the robots meta-tag) will be generated – and served – only for pages and posts which are saved after plugin installation. 
You have to open and save an older post or page if you want to generate the meta data for the particular content. 
For now there is no way to do this automatically.
The administrator can allow ordinary authors to change META informations or not. 
Even if changing is disallowed an author can see the keyword density and can be guided from the statistics while he is writing the content. 
He can do the on-page search engine optimization incidentally by knowing which keyword density should be reached. 
This makes SEO easier for authors.
Learn more about this plugin on <a href="http://www.keyword-statistics.net/wordpress-plugin.html" rel="nofollow ugc">keyword statistics plugin</a> – <a href="http://www.keyword-statistics.net/de/wordpress-plugin.html" rel="nofollow ugc">german</a>

Keyword Statistics

This SEO plugin checks the content of posts/pages for the keyword density (single/phrases) while writing and is automatically setting the META-tags.

husani

Searches various data sources (Google Blog Search and Twitter) for posts related to your content and displays links/summaries on your page or 
inside your posts. These links and summaries can be displayed anywhere and any way you wish — below your post, in a sidebar, etc. With the 
magic animation power of jQuery, SMIRC content can be hidden until a user clicks the customizable header.
SMIRC performs related content searching (at least in this version) by creating RSS feed URLs for the various data sources. The RSS feed is 
parsed and converted into XHTML for display in your blog.
All PHP is separated into logical classes and files, and all XHTML is standards-compliant. Lists of links, authors, and summaries are built 
using standard UL and LI tags, and can be modified to fit your theme via two CSS files contained within this plugin.
SMIRC is released to the WordPress community under the GPL. Please feel free to modify as you see fit, and if you find this plugin useful, donate 
to the author. All feedback is welcome at wordpressplugins@husani.com, and you can visit the author’s websites at http://www.husani.com and 
http://www.evb.com.
UPDATE FOR v1.1: Fixed a bug with setting header text.

Social Media Integrated Related Content (SMIRC)

Like trackbacks, but not -- this plugin searches and displays content related to your CONTENT, not just posts that link to yours.

Keyword Statistics vs Social Media Integrated Related Content (SMIRC)