Programmable Web is a:
web-as-platform reference site and blog delivering news, information and resources for developing applications using the Web 2.0 APIs. [ProgrammableWeb: About]
It includes a list of APIs, a list of mashups, and other stuff. The list of APIs includes the Library of Congress SRW interface, described as ‘information database search’.
Of course, as what it promotes becomes more widespread, this site becomes less feasible as it will be difficult for the lists to keep up with what is happening.