Alex Sawallich

This plugins enables the famous Google +1-button in your wordpress-installation. The button is shown beneath 
your posts/pages. With this button you can share the permalink to your post/page in your Google+ profile.
You’ve got the possibility to change the look of the button in the same manner, that you can do by using the 
configurator that Google provides: see <a href="http://www.google.com/webmasters/+1/button/" rel="nofollow ugc">Google plus one</a>.

Google+ One Button

Provides a +1 button from Google+ beneath each post/page.

Ryan Hellyer

Metronet AS

This plugin makes it easy to add a Google+ post to your WordPress post or page. It’s as easy pasting URL of the post onto it’s own line.
<h3>Credits</h3>
Thanks to the following (in no particular order) for help with the development of this plugin:
<ul>
<li><a href="https://plus.google.com/106908591930273336258/posts" rel="nofollow ugc">Petter El Fakiri</a> – Made the initial plugin suggestion</li>
</ul>

Metronet Embed Google Plus

Easily embed Google+ posts into your pages

Google+ One Button vs Metronet Embed Google Plus