Jesper Johansen (jayjdk)

Twitter Profile Field is a simple WordPress plugin that gives the user a new field in the profile page to add in their Twitter username.
The pluhin also provides a shortcode which allows authors to display their, or others, Twitter usernames, optionally with a link, in posts, pages, and text widgets.

Twitter Profile Field

Adds an additional field to the user profile page where the user can enter their Twitter username.

BuddyDev

Brajesh Singh

WordPress Username availability checker for WordPress & BuddyPress checks for the username availability on new user registration screens. 
It assist users & site admins by notifying them using ajax whether the username they entered is available or not.
<h4>Features</h4>
<ul>
<li>Checks for username availability in WordPress Admin New User screen</li>
<li>Checks for username availability on WordPress standard registration page</li>
<li>Checks for availability on BuddyPress registration page.</li>
</ul>
For screenshots & more details, please visit <a href="http://buddydev.com/plugins/bpdev-username-availability-checker/" title="Plugin page" rel="nofollow ugc">BuddyDev Username Availability Checker plugin page</a>
Free & paid supports are available via <a href="http://buddydev.com/support/forums/" title="BuddyDev support forums" rel="nofollow ugc">BuddyDev Support Forum</a>. Please Use BuddyDev support forums for your support requests. We may not be able to keep an eye over WordPress plugin support forum.

WordPress Username Availability Checker

WordPress Username availability checker checks if a username is available or not.

Twitter Profile Field vs WordPress Username Availability Checker