The Shutterstock API has been used by over 10,000 developers. The company includes names like Google, Facebook, and IBM in its list of developer partners. To offer these partners an additional revenue stream through the Shutterstock API, Shutterstock has launched self-serve API subscription plans.
Online bookseller Erapublications has an API for its in2Era web service for selling ebooks through online distributors. According to its documentation, this RESTful API, which requires an authentication key, integrates its catalog onto your site. Distributors get a cut of the sales.