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.

Artberri

Karmacracy is an easy way to know people sharing relevant content around your social networks, it’s a new generation URL shortener.
This wordpress plugin will allow you to generate and insert short URLs from this service onto a post or page, resumes your Karmacracy profile in a dashboard widget and allows you to share your published posts on Facebook or Twitter.
This plugin doesn’t automatically generate short links, but allows you to insert short links at will from the post editor.
FEATURES:
<ul>
<li>Panel for setting the Karmacracy configuration</li>
<li>Shortcode icon for easy insertion into a post or page</li>
<li>Dynamically generates and inserts links onto a post or page</li>
<li>Dashboard widget that resumes your Karmacracy profile</li>
<li>Option to share your posts on Twitter and Facebook when are published</li>
</ul>
Comments, questions, feature requests and bug reports are welcome: <a href="http://www.berriart.com/en/wp-karmacracy/" title="WP Karmacracy" rel="nofollow ugc">http://www.berriart.com/en/wp-karmacracy/</a>

WP Karmacracy

Allows you to insert Karmacracy links into posts or pages and share your posts on Facebook and Twitter.

Twitter style links vs WP Karmacracy