What Makes a Great Open API?
Viralheat Developer Center
They now provide free developer access – 5,000 calls to their sentiment analysis API/day.
History Of The Stack Exchange API, Mistakes
Worth reading if you work on or with APIs at any level.
Real Time Congress API
“a RESTful API over the artifacts of Congress, in as close to real-time as possible.” The API covers the current and previous sessions of Congress, but is not an archival site.
A “database of over 2000 open web APIs and thousands of applications people have built with them “