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.

Yatko

statistX PageRank displays the Google (TM) PageRank of your WordPress blog. 
The widget is automatic and can be configured to display different button styles.
Visit <a href="http://pr.statistx.com/pagerank-display.php" rel="nofollow ugc">Free pagerank Display</a> for details.

PageRank

statistX PageRank displays the Google (TM) PageRank of your WordPress blog.

Most Comments vs PageRank