DrKnown

<ul>
<li>Save and tag keywords</li>
<li>Create keyword lists (e.g., per post, product, or campaign)</li>
<li>Generate long-tail ideas from built-in or custom modifier banks</li>
<li>Add batches of keywords to a list with one click</li>
</ul>

Rocket Keyword Organizer

Organize saved keywords into lists, tag them, and generate long-tail variants from modifier banks—right inside WP admin.

littlejon

LJ Longtail SEO is a tool that detects search engine visits and uses this information to display a list of links based on second page search results.
The results in the database are aged off based on customizable settings so that once your longtail keywords have been boosted they will fall off the list and give way for other searches.
Admin interface has an optional keyword report that can be turned on via an option (On a large blog it is possible that there could be a performance hit on the admin page when using this option. Please note this will not slow down the blog side, just the admin page.). The keyword report will show the Top 100 keywords ordered by popularity and also showing the number of times the keyword has occurred.
As of Version 1.5 the plugin you can now add keywords to an Ignore list. This means if you don’t want a certain keyword registering as a referred search term you can simply put the phrase into the Ignored Keywords list and it will no longer register.
A widget will display a list of the popular searches that have come from search engine result pages beyond the first and provide a link on your sidebar back to the pages found.
Using this method can help to increase traffic to a blog via bring more importance to the Longtail keywords that can be used to find a site.
The original idea for this plugin was taken from <a href="https://wordpress.org/extend/plugins/seo-booster-lite/" title="SEO Booster Lite" rel="ugc">SEO Booster Lite</a> and <a href="http://www.thegooglecache.com/advanced-white-hat-seo-techniques/second-page-poaching-adanced-white-hat-seo-techniques/" title="Second Page Poaching - Advanced White Hat SEO" rel="nofollow ugc">Second Page Poaching – Advanced White Hat SEO</a>. I used the other plugin for a short period of time and didn’t like a few of the restrictions. Therefore I decided to make my own, there will be no Pro version or paid version. The version I release here is in production on my main blog. Any updates I make there will end up here including bugfixes.
This plugin currently only registers search results from Google, Bing, Yahoo, and Ask. It is compatible with both of Googles current referrer information meaning you should always have accurate SERP positioning results.

LJ Longtail SEO

LJ Longtail SEO is a tool that detects search engine visits and uses this information to display a list of links based on second page search results

Rocket Keyword Organizer vs LJ Longtail SEO