Bitly - Get the most out of your social and online marketing efforts. Own, understand and activate your best audience through the power of the link with Bitly Enterprise.
Kutt.it - Kutt.it is a free and open source URL shortener with custom domains and stats.
Diksi - Diksi is a Free custom URL Shortener with advanced links tracking, Links grouping and Link Management Platform.
YOURLS - YOURLS is a website that contains all the tools you need to create and launch your very own URL shortener. URL shorteners like bitly or TinyURL are fine for public use, but they offer limited options in terms of URL customization.
Lstu - A nice and open source url shortener. You can use it as service or install it on your own server.
Polr - An open source URL shortener. A great non-profit and free alternative to bit.ly, TinyURL, or goo.gl.