Andrew Norcross

Creates a YOURLS generated shortlink on demand or when saving posts.
Features:
<ul>
<li>Optional custom keyword for link creation.</li>
<li>Will retrieve existing URL if one has already been created.</li>
<li>Click count appears on post menu</li>
<li>Available for standard posts and custom post types.</li>
<li>Optional filter for wp_shortlink</li>
<li>Built in cron job will fetch updated click counts every hour.</li>
</ul>

YOURLS Link Creator

Creates a custom short URL when saving posts. Requires your own YOURLS install.

Boone Gorges

<a href="http://yourls.org/" title="Your Own URL Shortener" rel="nofollow ugc">YOURLS</a> is a free URL shortener service you can run on your webhost to have your own personal Bitly.
This plugin is a bridge between <a href="http://yourls.org/" title="Your Own URL Shortener" rel="nofollow ugc">YOURLS</a> and your blog: when you’ll submit a new post or page, your blog will tap into YOURLS to generate a short URL for it.
This plugin also features BuddyPress support. Short URLs can be generated automatically for each member and each group, and are customizable if permitted by the BuddyPress administrator.
Requires PHP 5.
Note: this plugin should still work but is no longer maintained. See http://yourls.org/#More#wordpress

YOURLS: WordPress to Twitter

Use YOURLS (a free GPL URL shortener service) to create short URLs of your posts, or for your BuddyPress groups and users

YOURLS Link Creator vs YOURLS: WordPress to Twitter