Add a sidebar widget showing top commentators in your WordPress site.
First install and activate Top Commentators Widget, now drag and drop (Dashboard ->Appearance ->Widgets) its widget to your sidebar.
It shows the top commentators of your blog using a sidebar widget. It is adapted from Show Top Commentators plugin at Personal Financial Advice. It is easy to manage from control form which means there is no need of editing PHP file; additional options are also available which makes it more flexible.