New York-based Betaworks today launched a useful–and cute–URL shortener, Bit.ly. The user-facing features, such as tracking clicks and cookie-based history of recent shortened URLs, are nice. Where Bit.ly really shines is the data it makes available via its simple API.
Without registering for an API key, developers can shorten URLs, expand previously-shortened URLs, and get data about a Bit.ly URL. The information Bit.ly makes available includes the number of clicks, the referring sources of those clicks, and three sizes of thumbnails of the resulting web page.
Bit.ly is a model platform, a great example of how to launch a service with an API.