bit.ly allows users to shorten, share, and track links (URLs). Reducing the URL length makes sharing easier. bit.ly can be accessed through our website, bookmarklets and a robust and open API. bit.ly is also integrated into several popular third-party tools such as Tweetdeck. A more full list of third party tools can be found on the bit.ly blog. Unique user-level and aggregate links are created, allowing users to view complete, real-time traffic and referrer data, as well as location and metadata. Tracking stats are available after users shorten their long links with bit.ly by clicking on the Info+ link on bit.ly, or just adding a + sign to the end of any bit.ly link - for example, http://bit.ly/n0og+
I have used this tool since I hopped on Twitter. I have thought about looking at other tools but haven't due to the stability & simplicity of this tool. It includes an api and analytics. Easy to integrate into Wordpress and other platforms that allow use of your own url shortener. Can't go wrong with this one peeps!