athakur

This plugin adds Google Plus One Button to every post on your WordPress Site. 
This plugin is simple and uses in built function to display Google Plus 
One Button below every post. The size property of the plugin is set to “standard” 
and the annotation property is set to “inline”. Read about these properties here 
https://developers.google.com/+/plugins/+1button/

WordPress Plus One Button

Peadig

Adds an unofficial Google+ Share button to any WordPress page, post or template.
<ul>
<li><a href="http://pleer.co.uk/wordpress/plugins/google-plus-share-button/" rel="nofollow ugc">Google Plus Share Button</a> Plugin homepage.</li>
<li>More <a href="http://pleer.co.uk/wordpress/plugins/" rel="nofollow ugc">WordPress Plugins</a>.</li>
</ul>

Google+ Share Button

Adds an unofficial Google+ Share button to any WordPress page, post or template.

WordPress Plus One Button vs Google+ Share Button