ichurakov

The Open Graph protocol enables any web page to become a rich object in a social graph. For instance, this is used on Facebook to allow any web page to have the same functionality as any other object on Facebook.
To turn your posts and pages into graph objects, the plugin add the following metadata to webpage header: 
og:title – The title of your post/page. 
og:description – The excerpt of your post/page. 
og:image – URL of featured image (if exists) which represent your post/page. 
og:site_name – The title of website. 
og:url – The canonical URL of your post/page.
Plugin support page: <a href="http://www.icprojects.net/open-graph-meta.html" rel="nofollow ugc">Open Graph Meta</a>.

Open Graph Meta

This plugin add Open Graph meta data to blog posts and pages.

Rami Yushuvaev

nielsvanrenselaar

This plugin lets you set the Open Graph meta tags per post, page or custom post type and set default start values for new posts. It’s a simple plugin to get you started with the Open Graph meta tags and will get extended features soon.

Open Graph Metabox

Better!

This plugin lets you set the Open Graph meta tags per post, page or custom post type and set default start values for new posts.

Open Graph Meta vs Open Graph Metabox