Our API directory now includes 195 science APIs. The newest is the AnnotQTL API. The most popular, in terms of mashups, is the NCBI Entrez API. We list 4 NCBI Entrez mashups. Below you'll find some more stats from the directory, including the entire list of science APIs.
Web APIs and mashups are not only of interest to the developer community. There are also research activities that look at how to improve various aspects of API design as well as services' and mashups' implementation and deployment. If you are interested in a cutting-edge research that may influence the future of Web APIs, then you should look at series of workshops on Web APIs and Service Mashups.