Institute for Social and Economic Research and Policy
The Institute for Social and Economic Research and Policy (ISERP) is a large and well-established interdisciplinary institute for social science research.
Because of its size and extensive interdisciplinarity, there's a non-trivial chance that if you're an undergraduate in a social science or a related field looking to work as a research assistant you'll end up employed by ISERP. It also offers an annual summer fellowship for undergraduates, which can be an excellent opportunity for students whose academic and career interests intersect with its mandate (see e.g. Jason Bello).
It boasts members from the faculties of the departments of "Anthropology, Economics, History, Political Science, Psychology, Sociology, and Statistics, as well as [the faculties] of Barnard College, the Earth Institute, Teachers College, the Mailman School of Public Health and the Schools of Architecture, Planning and Preservation, Business, International and Public Affairs, Law, and Social Work."