dantaylorseo

This plugin adds a ‘Add [author_name] on Google+’ button to the end of every post. Simply add your Google+ ID to the ‘Your Profile’ area of the Admin.
<ul>
<li><a href="http://www.seowned.co.uk/wordpress-plugins/add-an-add-to-circles-button-to-your-wordpress-posts/" rel="nofollow ugc">Google+ Author Button</a> plugin homepage.</li>
<li><a href="http://twitter.com/dantaylorseo" rel="nofollow ugc">Follow @DanTaylorSEO on Twitter</a>.</li>
</ul>

Google+ Author Button

This plugin adds a 'Add [author_name] on Google+' button to the end of every post.

acbaltaci

The simple and 100% working way of google +1 share button. It uses google external api to call. 
Please visit http://www.allthemesnulled.com for demo.

Google Plus Share and +1 Button

This plugin puts a google+ share button on top of posts.

Google+ Author Button vs Google Plus Share and +1 Button