Alex Moss

Google+ comments was introduced in April 2013 to blogger.com users. This plugin lets you add Google+ comments to your WordPress site!
Simply install the plugin and follow the instructions on the Settings page.
<ul>
<li><a href="http://3doordigital.com/wordpress/plugins/google-plus-comments/" rel="nofollow ugc">Google+ Comments</a> Plugin homepage.</li>
<li>More <a href="http://3doordigital.com/wordpress/plugins/" rel="nofollow ugc">WordPress Plugins</a>.</li>
</ul>
You can also insert the comment box as a shortcode into any post, page or template and use your own settings for each time you do it! Simply use the shortcode [gp-comments]

Google+ Comments

The Google+ Comments WordPress plugin makes it easier for you to setup, administer and customise Google+ comments from your WordPress site.

Thorsten Ott

BIG WARNING: This is still in early development and needs testing.
This plugin lets you implement a cookie based front-end authorization system that can be used (for example) to allow users who are logged in via an system to comment on your site.
Please see the inline documentation for the various filters this plugin provides to alter it’s behaviour.

FrontEnd Cookie SSO

This plugin lets you implement a cookie based front-end authorization system that can be used (for example) to allow users who are logged in via an sy …

Google+ Comments vs FrontEnd Cookie SSO