gentlesource

This plugin creates a short URL from the blog post permalink and stores it 
in the database. The URL is displayed below the blog post along with a link 
to twitter that passes the short URL on.
You can use all short URL services that offer an API. Here are a few:
<ul>
<li>http://melt.li/</li>
<li>http://lin.io/</li>
<li>http://unrelo.com/</li>
<li>http://bit.ly/</li>
<li>http://u.nu/</li>
<li>http://tinyurl.com/</li>
</ul>

GentleSource Short URL

Automatically shortens the blog post URL.

k0nsl

This plugin creates a short URL from the blog post permalink and stores it in the database. The URL is displayed below the blog post along with a link to twitter that passes the short URL on, if defined in the settings page. The plugin currently use knsl.net as the only service and stores the data in the database of knsl.net.
Plugin homepage: http://k0nsl.org/blog/k0nsl-short-urls-plugin/
For support use WordPress.org or devNET community forums: http://devnet-software.org/
Thanks!

k0nsl Short URLs

Automatically shortens the blog post URL via knsl.net.

GentleSource Short URL vs k0nsl Short URLs