The Comments Evolved plugin easily integrates a more robust commenting system into WordPress. It allows the users to comment from their favorite social media accounts, instead of having to create a WordPress account on the user's site.The plugin also prevent spam comments on the user's WordPress site by forcing visitors to use their social media accounts instead of just a dummy account they create.
Disqus is a popular service for web comments and discussions. Disqus makes commenting easier and more interactive, while connecting websites and commenters across a thriving discussion community.
IntenseDebate is a commenting tool which integrates with popular CMS platforms and offers features such as Threading, Email notifications and reply by email. The users can post via their social accounts, as a guest or integrate with the user's existing sign up process. It has strong Anti-Spam options powered by Akismet.
Jetpack Comments replaces the user's default comment form with a new comment system that has integrated social media login options. It allows the users to comment on the post by simply logging-in through their social media accounts.