Matheus Eduardo

This plugin adds a new field (metadata) in the section editing links in order to add social networking links (like <a href="http://twitter.com/" rel="nofollow ugc">twitter</a>, <a href="http://flickr.com/" rel="nofollow ugc">flickr</a>, etc.) to any link.
PT-BR 
Este plugin acrescenta um novo campo (metadados) na seção de edição de links para poder adicionars links de redes sociais (como <a href="http://twitter.com/" rel="nofollow ugc">twitter</a>, <a href="http://flickr.com/" rel="nofollow ugc">flickr</a>, etc) a um link qualquer.

Simply Social Links

This plugin adds a new field (metadata) in the section editing links in order to add social networking links (like twitter, flickr, etc.) to any link.

yanniks

This is the Shariff for WordPress plugin based on c’t Shariff.
For more information, check out the original <a href="https://github.com/heiseonline/shariff" rel="nofollow ugc">GitHub project</a> and the <a href="http://ct.de/shariff" rel="nofollow ugc">c’t information page</a>.
<blockquote>
Shariff enables website users to share their favorite content without compromising their privacy.
Facebook, Google+ and Twitter supply official sharing code snippets which quietly siphon personal data from all page visitors. Shariff enables visitors to see how popular your page is on Facebook and share your content with others without needless data leaks.
Shariff <code>(/ˈʃɛɹɪf/)</code> is an open-source, low-maintenance, high-privacy solution maintained by German computer magazine c’t and heise online.
</blockquote>
Shariff supports sharing buttons for Facebook, Twitter, Google+, LinkedIn, Pinterest, Reddit, StumbleUpon, XING, WhatsApp and mail. 
Select which color you want, set the button location, select the orientation fitting most to your website and set the TTL just as you want.

Shariff for WordPress

Shariff enables website users to share their favorite content without compromising their privacy.

Simply Social Links vs Shariff for WordPress