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.

Julio Potier

AutoShortener can create short links in your WordPress website for your posts and pages but also for external links. 
You got many many great options, a usefull admin panel, bookmarklets, shorcodes. 
But easy to use ! Visit website www.autoshort.com for more informations.

BAW AutoShortener

AutoShortener can create short links in your WordPress website for your posts and pages but also for external links.

Custom Shortlink Domain vs BAW AutoShortener