http://bit.ly/ is a URL-shortener with lots of new stuff designed for an app developer who needs everything and more!
1. History — remember the last 15 shortened URLs you’ve created. They’re displayed on the home page next time you go back. Cookie-based.
2. Click/Referrer tracking — Every time someone clicks on a short URL we add 1 to the count of clicks for that page and for the referring page.
3. There’s a simple API for creating short URLs from your web apps.
4. Automatically create three thumbnail images for each page you link through bit.ly, small, medium and large size. You can use these in presenting choices to your users.
5. Automatically mirror each page, never know when you might need a backup.
6. Most important for professional applications, you can access all the data about each page through a simple XML or JSON interface. Example.
7. All the standard features you expect from serious url-shorteners.