WP Comment Remix adds a plethora of new options and features to Wordpress. From Reply and Quote links for commenters, to a full upgrade to the edit comments pages in the admin panel, WPCR will save you time and effort when running your blog.
http://pressography.com/plugins/wp-comment-remix/
WP Comment Remix is also my entry for the WeblogToolsCollection.com Plugin Compeition:
http://weblogtoolscollection.com/pluginblog/2008/05/30/wp-comment-remix/