bitly
bitly (formerly bit.ly) is a URL shortening and bookmarking service

lilURL
lilURL is a simple PHP/MySQL script for generating lil´ URLs. It's similar to TinyURL, Shorl, MakeAShorterLink, etc, but you can run it on your own server . Requires PHP and MySQL; supports mod_rewrite.
Url Pal
Do you already have a short, easy to remember domain name and have no idea what to do next? We’ve got a solution! Start your own service like tinyurl.com or bit.ly. Within 5 minutes You’ll be able to start such a site and generate huge traffic and income. Imagine, generating thousands of...
YOURLS
YOURLS is a small set of PHP scripts that will allow you to run your own URL shortening service (a la TinyURL). You can make it private or public, you can pick custom keyword URLs, it comes with its own API. You will love it.