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.

clint.s

Love WordPress? Love Bitly? After installing this plugin, you’ll be able to shorten a link and view clicks right from WordPress. Your new links will be saved to Bitly for reference and deeper analysis.
To do that, you must have a Bitly account to use the plugin. Your account is where you store, edit, and view metrics for your links. Register at bitly.com.
No matter the type of site you own (from a personal blog to an ecommerce store and everything in between) Bitly makes it easy to create shorter links and keep an eye on your clicks. Whether you share your links on social, SMS, or email, a short link is easier to manage and remember.

Bitly's WordPress Plugin

Simple & awesome Plugin :-) 
Easy to Configure it with Bitly.


Much Needed Plugin

Create short links to your content with Bitly’s WordPress Plugin.

GentleSource Short URL vs Bitly's WordPress Plugin