Nader

The “Most Comments” plugin displays as the name says posts with the most comments. You can either use the widget in the sidebar or integrate the plugin as template tag in your theme files.
Features:
<ul>
<li>Limit the amount of posts to be shown</li>
<li>Show comments from a specific post category</li>
<li>Exlude posts without comments</li>
<li>Select a time range (last XX days) of posts to be taken into account</li>
<li>Customize the design template via the settings page</li>
<li>Place a widget in your sidebar</li>
</ul>
More Information & Feature Description: 
http://www.brandinfection.com/wordpress-plugins/most-comments/
<h3>Configuration</h3>
You can configure the most comments plugin to your needs. Options can be found under the menu <code>Settings > Most Comments</code>

Most Comments

Display posts with the most comments, as a widget or on a page using the template tag. Customize the look with specific settings.

Frank Neumann-Staude

polyres

Ulf Schönefeld

This plugin/add-on requires the plugin GamiPress(WordPress plugin repository)!
This free plugin/add-on extends the GamiPress Plugin, so you can react to the following WordPress events in GamiPress
<ul>
<li>user_register</li>
<li>
delete_user
</li>
<li>
add_attachment
</li>
<li>delete_attachment</li>
<li>
edit_attachment
</li>
<li>
trashed_post
</li>
<li>untrashed_post</li>
<li>
delete_post
</li>
<li>
trashed_page
</li>
<li>untrashed_page</li>
<li>
delete_page
</li>
<li>
trashed_comment
</li>
<li>untrashed_comment</li>
<li>delete_comment</li>
</ul>

Extend GamiPress

Awesome work guys!

You are the first 3rd party plugin for GamiPress on WordPress.org, so, congratulations and thanks!

Just let you know that the user_register event is already handled on GamiPress so if you want, you can remove it in order to avoid a duplicated event

Awesome!

Extends the GamiPress Plugin for WordPress System Hooks

Most Comments vs Extend GamiPress