DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
IntenseDebate - IntenseDebate's comment system enhances and encourages conversation on your blog or website.
Commento - A fast, bloat-free comments system to foster discussion on your website
Thrive Comments - Thrive Comments is a comment system for Wordpress.
Commentbox - Commentbox is a jsf component that allows quick realization of a comment functionality
Viafoura - Viafoura is an easy-to-integrate social monetization platform that enables your to better engage, understand and monetize your community.