This plugin adds a new widget which can show statistics for your blog’s/forum’s 
Disqus comments: most popular discussions, top commenters, recent comments.
Configurable are: 
 * Color Theme 
 * Number of items to show 
 * Default tab view (most popular discussions, top commenters, recent comments) 
 * Whether to show the standard WordPress widget title bar 
 * Title of the widget in the title bar

Disqus Widget

Allows the user to display statistics for their blog's/forum's Disqus comments.

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 Widget vs Disqus Popular Threads Widget