TentBlogger Simple Top Blog Commenters plugin is a simple way to show your appreciation for your community is to display a list of the top commenters on your blog’s sidebar. Not only does it give them some link love back to their property but it also shows new visitors that there are conversations happening as well!
Lightweight and well coded. Low cost in terms of page load speed!
Can choose to show a particular “Date Range” such as Weekly, Monthly, or All Time!
Direct link to commenter’s URL for some link love!
Option to show Gravatar
Option to hide the total amount of comments
Easy to customize via CSS for your own blog
Download and info: http://wordpress.org/extend/plugins/tentblogger-simple-top-blog-commenters/