Salar Gholizadeh

Want to display precise related posts from your website without manually selecting posts?
Ultimate Related Content plugin gives smartly-chosen related posts from your website using an effective mixture of factors from tags, categories, and entry titles.
You can easily controll how many related entries to show on each page and other settings from 
related content section in WordPress’s native customizer panel.
With minimum impact on your website performance, you can also choose whether to show posts statically or via 
Ajax calls.

Ultimate Related Content

If you're looking for a smart and quich way to display related posts from your blog, then Related Content could be the right choice.

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.

Ultimate Related Content vs Social Media Integrated Related Content (SMIRC)