There are too many url shortner services available today. As you know bit.ly, Tiny URl, tr.im are some of them. below is a list of some URL shortening services

1. bit.ly

2. tinyurl

3. su.pr

4. tr.im

5. cli.gs

6. twurl

if you would like to run a url shortener of yourself here are some. Your hosting should support PHP and MySQL

1. Yourls

2. Shorty

You can read about 7 of this type here