Steve

This plugin allows you to specify an alternative domain name to use with the built in URL shortening service.
For this to work it requires the chosen domain to be pointed / parked on the hosting account used for your blog.

Custom Shortlink Domain

Customise the domain name used to generate shortlink URLs.

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.

Custom Shortlink Domain vs Bitly's WordPress Plugin