I run a Christian news portal at theophiles.org, which allows comments on the various news stories which are submitted. The previous iteration of this site had a custom Top 10 list, showing the most popular articles, and the most prolific commenters. To reproduce this feature in Joomla, I created two modules.
The Top Commenters module requires the !JoomlaComment module to enable comments on your site.
The Top News Submitters module does not require any other modules.
View a demo. These modules are displayed at the bottom of the main content area.