xdark

Easy Related Posts is a WordPress plugin that displays posts related to the one a user is currently reading. 
Easy Related Posts can display related posts in main content area or in sidebars through a widget. 
Equipped with 3 eye catching fully responsive themes, supports basic modifications on them from admin panel. It also has a theme system that let you modify or write your own themes to match you personal needs. 
Through an intuitive algorithm it creates “relations” between posts and rates them based on posts categories and/or tags in a way so these ratings are as much as accurate they can be. 
Last but not least in any way, Easy Related Posts uses the best coding standards and practices with mind in security.
If you like this plugin please support the developers. You can do so using the links inside plugin settings page or by purchasing the PRO version.
PRO version can be purchased from <a href="http://erp.xdark.eu/downloads/easy-related-posts-pro/" rel="nofollow ugc">here</a>. 
To see a full list of features and compare them to the PRO version please visit <a href="http://erp.xdark.eu/version-comparison/" rel="nofollow ugc">this page</a>.
Easy Related Posts wont spam your visitors with content from other sites, ads or in any other way.
<a href="http://erp.xdark.eu/demo/" rel="nofollow ugc">See the demo</a>
This plugin requires PHP version 5.3 and above.
Features:
<ul>
<li>Easy to setup</li>
<li>Choose displayed content: excerpt length, thumbnail resizing and many more.</li>
<li>Choose if related posts should be fetched by categories or by tags</li>
<li>Exclude posts that have certain categories and/or tags from related posts</li>
<li>Prevent related posts from spawning in certain categories or tags</li>
<li>Display related posts as an eye-catching pop up block</li>
<li>Display related posts through a widget or/and in main content area</li>
<li>Options optimized before activation for most of the cases</li>
<li>Really fast, not a single database entry (I really love clean DB’s)</li>
<li>Responsive design</li>
</ul>
Please report any bugs or features you’d like to see in feature releases <a href="http://erp.xdark.eu/bugs/set_project.php?project_id=3" rel="nofollow ugc">here</a>

Easy Related Posts

Displays related posts in the end of each post or/and in sidebar through a widget

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Display a list of related posts along with thumbnail images of those posts for the current post.
You can select the number of posts to be display on articles or on feed.
You can choose to exclude posts from certain categories as well as exclude pages.
<h4>Features</h4>
<ul>
<li>Display Related Posts with thumbnail image automatically in content / feed, no need to edit template files </li>
<li>Doesn’t use any custom field to generate thumbnail images </li>
<li>You can manually add code to your template where you want the Wp-thumbie to be displayed </li>
<li>Exclude posts from categories </li>
<li>Exclude display of thumbnail related posts on Pages </li>
<li>Exclude pages in thumbnail related Posts list </li>
<li>Related posts based on content and post title </li>
<li>Set thumbnail image size (width & height)</li>
<li>Turn on/off post excerpt (automattically extracted from posts)</li>
<li>set length of post excerpt </li>
<li>Different styling for displaying thumbnail related posts </li>
<li>Display Thumbnail related posts in RSS Feeds (Styling issue)</li>
<li>To use images from external sites you must set ALLOW_ALL_EXTERNAL_SITES to True in timthumb.php (use it as your own risk)</li>
</ul>
<h3>How to Upgrade</h3>
<ol>
<li>
If you have modified stylesheet (wp_thumbie_verticle.css) then make sure to backup that file first.
</li>
<li>
Once you have backup files use WrodPress plugin upgrade option to upgrade to latest version.
</li>
</ol>

Wp-Thumbie – Related Posts with thumbnails for WordPress

Show user defined number of related / similar posts with thumbnail image

Easy Related Posts vs Wp-Thumbie – Related Posts with thumbnails for WordPress