Dan Cohen over at George Mason University looked that APIs listed here and asked a good question: Where Are the Noncommercial APIs?. He makes a number of valid points here:
One of my pet peeves as someone trying to develop software tools for scholars, teachers, and students is the lack of application programming interfaces (APIs) for educational resources...Now a clearing house for APIs [ProgrammableWeb] shows the extent to which noncommercial resources—and especially those in the humanities—have been left out in the cold in this promising new phase of the web. Count with me the total number of noncommercial, educationally-oriented APIs out of the nearly 200 listed on Programmable Web.
That's right, for the humanities the answer is one: the Library of Congress's somewhat clunky SRU (Search/Retrieve via URL). Maybe in a broader definition you could count the API from the BBC archive, though it seems to be more about current events. The Internet Archive's API is currently focused on facilitating uploads into its system rather than, say, historical data mining of the web. A potentially rich API for finding book information, ISBNdb.com, seems promising, but shouldn't there be a noncommercial entity offering this service (I assume ISSNdb.com will eventually charge or limit this important service)?
By my count the only other noncommercial APIs are from large U.S. government scientific institutions such as NASA, NIH, and NOAA. Surely this long list is missing some other APIs out there, such as one for OAI-PMH. If so, let Programmable Web know—most "Web 2.0" developers are looking here first to get ideas for services, and we don't need more mashups focusing on the real estate market.