There aren't many independent sources covering "Cloud APIs" - whether referring to "Independent" groups, standards bodies, or specific providers. This lack of sources without an agenda of some type makes it incredibly difficult to bring together good information that isn't somehow tainted. By creating this new Wikipedia entry, the hope is that a solid, independent, and over-arching resource can be created for the community to share. The cloud computing concept covers a broad range of topics, and therefore this Cloud API entry covers a broad range of available APIs.
The Cloud APIs are broken up into two Primary types, each having three sub-types. Think of a 2 row by 3 column grid (I will be updating this post and likely the Wikipedia article with a table of this sort, attempting to begin classifying of each Cloud API as time permits). The rows consist of Cloud Provider Cloud APIs and Cross Platform Cloud APIs, while the columns consist of Infrastructure (think IaaS), Services (think PaaS), and Applications (think SaaS). These categories (or combinations of them in specific cases) should allow for the classification of all current Cloud APIs and provide for a common understanding in the industry.
Please view or review the Wikipedia entry for Cloud APIs (which can be found at http://en.wikipedia.org/wiki/Cloud_APIs). Everyone is encouraged to go and take a look, edit carefully, and contribute thoughtfully to this effort as the more information that is put in, the more the community will get back out.