Intense Debate

What about IntenseDebate it’s a feature-rich comment system with automated installation for WordPress and many other blogging/CMS platforms. IntenseDebate offers numerous features that improves the commenting experience, like the reply by email functionality, open-id support, hardcore moderation and blacklisting, RSS readers and tracking, email notifications, an ability to integrate Facebook and Twitter accounts with your comments so that you can send your comments to your Facebook and Twitter profiles letting your followers know you commented on a post. In addition, IntenseDebate has recently added a few plugins such as Seesmic for video comments, smileys, embedding YouTube videos and enabling PollDaddy plugin to create polls in comments.