The database available on this site "provides information on the status of over 500 major multilateral instruments deposited with the Secretary-General of the United Nations (including the texts of reservations, declarations and objections) and covers a range of subject matter such as Human Rights, Disarmament, Commodities, Refugees, the Environment and the Law of the Sea."
"Treaties in Force is prepared by the Department of State for the purpose of providing information on treaties and other international agreements to which the United States has become a party and which are carried on the records of the Department of State as being in force as of its stated publication date..."
Good for reviewing the legal structures of different countries.
"GlobaLex is an electronic legal publication dedicated to international and foreign law research. Published by the Hauser Global Law School Program at NYU School of Law, GlobaLex is committed to the dissemination of high-level international, foreign, and comparative law research tools in order to accommodate the needs of an increasingly global educational and practicing legal world."
Also produced by ASIL, EISIL is "an open database of authenticated primary and other materials across the breadth of international law, which until now have been scattered in libraries, archives and specialized web sites."
Excellent place to start to get an overview of primary documents related to areas of international law.