Mashups. To be able to think creatively about it you must know which sites offer an API. And then; what kind of data you can expect to be able to access. Here is a list of websites which offer an API. Some are the most popular, but you will find a little golden egg or two in this list.

Facebook have an API, you can use most of the data users have stored at facebook, like friends, profile info, photos.
API Docs: Facebook API Documentation

From Twitter you can get the user data, followers, friends and status updates. A previous article on this website was about Twitter applications.
API Docs: Twitter API Documentation

With the last.fm API you can retrieve user data, most popular songs and everything stored within last.fm

A friend of mine created this mashup of Spotify and Last.fm.
API Docs: Last.Fm API Documentation

With the bit.ly API you can expand and shorten URL’s, then gather statistics about traffic on those specific short URL’s.
A lot of Twitter users post links shortened with bit.ly, so it would also be possible to keep track of what’s popular by the use of this API.
API Docs: Bit.ly API Documentation

Create your own maps, you can use Google Maps API to display geodata in your mashup.
API Docs: Google Maps API Documentation

GeoNames
With the GeoNames API you can get data for your Google Maps; Airports, Hotels and a lot of other things. Trivial resource!
API Docs: GeoNames API Documentation

With the Digg.com API you can get current popular stories from all categories, the digg count, comments and a lot of other data.
API Docs: Digg.com API Documentation

That’s the list!

Which other popular APIs exist? If you have used another API, leave a comment!

Tags: api, bitly, digg, facebook, geonames, google maps, last.fm, mashups, Twitter