godthor

This will create a new widget which will display your most popular posts and pages based on comment count with Disqus. Alternatively, you can use a shortcode as well.
It’s very simple to use. Just drag the widget into a sidebar and configure it, or visit the settings under the WordPress Settings menu.
Just Some of the Options:
<ul>
<li>Show featured image.</li>
<li>Choose featured image size.</li>
<li>Choose featured image alignment.</li>
<li>Show the post date.</li>
<li>Select how many days to check, IE: past 90 days.</li>
<li>Set how many posts to show.</li>
<li>Save the results for faster loading.</li>
<li>Load results using Ajax. Perfect to avoid caching results.</li>
</ul>
Note: This plugin requires you have an application registered with Disqus: https://disqus.com/api/applications/ 
It’s free and simple to setup, just follow that link.

Disqus Popular Posts

Creates a widget to show the most popular posts and pages on your site based on Disqus comments. Can also be used with a shortcode.

Ron Zvagelsky

Integrates with the Disqus API to show your most popular threads (most commented posts). Can be added via sidebar widget, template tag, or shortcode.
<a href="http://presshive.com/plugins/disqus-popular-threads-widget-for-wordpress/" rel="nofollow ugc">For more information or to request additional features, please visit the plugin page</a>

Disqus Popular Threads Widget

Shows your most commented posts from Disqus via widget, shortcode, or template tag.

Disqus Popular Posts vs Disqus Popular Threads Widget