georf

This plugin uses JavaScript to verify that commentators are persons rather than bots.
If a user’s browser doesn’t support or allow JavaScript, so-called CAPTCHAs are used. The commentator has to enter a fruit name given as image before sending his or her comment.

Obstcha

Decent comment verification to avoid spam without user interaction.

OpenWeb Admin

Comments Evolved ( formerly Google+ Comments for WordPress ) makes the comment section tabbed seamlessly adding tabs for G+ Comments, Facebook, Disqus, WordPress Comments, and Trackbacks
If a user is required to create an account with your site before they can comment, you might as well ask them to fetch you a soda from mars. It’s probably not going to happen. However, if you can give them the option to comment with an account they’ve already set up, then you will be much more likely to get some interaction.
**Source Code @ Github: ** <a href="https://github.com/bholtsclaw/comments-evolved" rel="nofollow ugc">comments-evolved@github</a>
Using this plugin or JavaScript to load comments does NOT have a negative effect on your SEO, Google now indexes content ( and specifically comments ) loaded via JavaScript. See <a href="http://blog.optimum7.com/safon/google/google-now-indexing-fb-comments.html" rel="nofollow ugc">this link</a> and also <a href="http://webmasters.stackexchange.com/questions/27042/effect-on-seo-of-lazy-scrolling-on-html-comments" rel="nofollow ugc">this one</a> for more details.
<ul>
<li>You should have <a href="http://plus.google.com/authorship" rel="nofollow ugc">Google Authorship</a> already setup and in use for your site.</li>
<li>I’ve setup a page so if you want to <a href="http://www.wepay.com/donations/brandonholtsclaw" rel="nofollow ugc">Donate</a> to this plugins development, now you can.</li>
</ul>
This plug-in is not endorsed or associated with the Google, Twitter, Disqus, Facebook, WordPress.org, Automattic, or WordPress HelpCenter.

Comments Evolved for WordPress

cool extension
Adds Google and Facebook in no time
Super simple to use!



Simple and nice looking

Comments Evolved ( formerly Google+ Comments for WordPress ) makes the comment section tabbed seamlessly adding tabs for Comments & More

Obstcha vs Comments Evolved for WordPress