The API landscape is extremely dynamic. The following 2 diagrams taken from ProgrammableWeb describe the most common APIs which are used in order to build mash-ups. They show the dominance of major historic players (check the “see all time” diagram) but also the more recent rise of new players such as Twilio in the recent past (last 14 days), as well as the convergence of Cloud Computing and Telecom.
As I started writing this article at the beginning of October 2011 , the http://www.programmableweb.com/ web site indicated on its home page that it has identified 4007 APIs and 6175 mash-ups on a global footprint: At the moment you are reading this piece on the Visionary Marketing, I am certain these numbers are completely outdated. I agree that, Dear Developers, these numbers are still very far from your ‘Ocean of Apps’ but this new ecosystem nevertheless starts to look like a ‘Jungle of APIs’.