The ProPublica Forensics API allows access to data from Propublica's investigation into the quality of autopsies across America. The API provides "state and county-level data about coroner and medical examiner systems in the United States." The RESTful API is available in JSON, XML and JSON-P formats. An astounding variety of data are available, from the ratio of autopsies to what is expected, to the number of uncertified pathologists working in a state or county system, and on and on.
RESTful services that underpin many Web APIs today should follow design patterns that make any Web API a good Web API. Such design patterns are all about respecting HTTP protocol specifications, respecting good URI design principles, or taking the full advantage of underlying Web infrastructure for Web API's good performance and scalability. If you are interested in such practices or in a cutting-edge research that may impact the future of Web APIs developments, you should look into the series of workshops on RESTful Design.