Speedboxer

This plugin will convert valid <a href="http://twitter.com/" title="Twitter" rel="nofollow ugc">Twitter</a> usernames mentioned in comments into a link to their Twitter profile page. For example, if somebody mentions “@mattfreedman” in their comment, this plugin will check with Twitter to see if the user “mattfreedman” exists (which is does) and when it does, it will convert it into “<a href="http://twitter.com/mattfreedman" rel="nofollow ugc">@mattfreedman</a>“.
Please note: As this plugin converts usernames on the fly (whenever and everytime somebody views the comments), and checks Twitter for every username (to ensure it’s valid), I strongly recommend using a caching plugin such as <a href="https://wordpress.org/extend/plugins/wp-super-cache/" title="WP Super Cache" rel="ugc">WP Super Cache</a>. Which will not only lessen the load on Twitter’s servers, but also speed up page loads.
Although it says this plugin requires WordPress 2.6, I see no reason why it wouldn’t work with earlier versions, I just haven’t tested it with earlier version.
This plugin requires cURL to be installed on your server, and has only been tested with PHP 5.2.x.

Twitter Links

Converts Twitter usernames mentioned in comments (eg. @mattfreedman) with a link to the mentioned user's Twitter profile page.

James Andrews

Full Circle’s primary purpose is to allow you to automate notifying your different social networks of new blog posts. Currently the only social networks that it connects to is Facebook and twitter. After simple configuration, any blog posts made on your blog will automatically posted as a link in your feed, and/or update your twitter status.
Also added are the ability to have links to facebook, twitter, digg, technorati and delicious all to the bottom of your blog posts. Allowing your blog readers to share your blog with their social networks.
Note: This version changes the database structure so that it can record better for more networks without changing the dbstructure in the future. Before upgrading please backup the fullcircle_posttracker database table in case upgrade fails as deactivating the previous version destroys this table. Newer versions will not, so that we can use old tables to move data around to new tables if needed

Full Circle

Full Circle allows you to connect your blog to your favorite social media by announcing your blog posts automatically for you.

Twitter Links vs Full Circle