The Google URL Shortener takes long URLs and creates short links on the goo.gl domain name. The REST-based API requires authentication with an API Key and Auth Token (OAuth).
Click the "Track this API" button on any profile page and never miss an API update, new app, or breaking news for that API again.
Nice and short api. I've posted a C# tutorial on my site on using this if anyone is interested: http://jarloo.com/code/api-code/google-url-shortening/