neon

If you write something like “@nick, how are you?” this plugin will search for @nick’s url in the comment list of the current post and will convert his/her name to a link.

Twitter style links

This plugin allows you to add Twitter style links to comments.

andeggs

ProSocial is a free WordPress plugin which connects your readers with your authors.
It shows an attractive pop-up bar next to your authors’ names, with links to their social media accounts.
On multi-author blogs, it’s a great way of encouraging your readers to connect with your authors on other social networks.
See it in action here: http://digitalshift.me/prosocial/
Features:
<ul>
<li>40+ social networks: You choose which networks to display. Your authors can add then their accounts themselves.</li>
<li>Includes email: Show your authors’ email addresses as well (with a captcha form to prevent spam).</li>
<li>Google Analytics: If you use Google Analytics, you can see who’s clicking on what.</li>
</ul>

ProSocial

ProSocial shows a pop-up bar next to your authors' names, with links to their social media accounts.

Twitter style links vs ProSocial