Business models were nascent in 2005, when ProgrammableWeb listed only 105 APIs in our directory. There were only four basic models, according to John Musser's talk this morning at Glue. Fast forward six years and those same business models exist, but there's a lot more detail, as the now 3,000+ APIs have refined the ways an API can make money.
2011 API Business Models (larger version)
Most of the 2005 models contain at least another level of detail, with the "developer gets paid" model containing the most granularity.
There's a lot of detail in that slide. Does it cover everything?
Musser's full slides are embedded below or you can view on SlideShare.