From Harvard Law School
Legal Research on International Law (U. Chicago Law Library) - very thorough review of Internet sources
NYU Law Library - International Law sources
Constitution Finder - web guide to constitutions of nations
Oxford International Encyclopedia of Legal History (3 vols) Schaeffer Law Library K 50 .O94 2009
Parry & Grant Encyclopaedic Dictionary of International Law Schaeffer Law Library KZ 1161 .P37 2009 (Also available online)
United Nations and International Law - good basic introduction to the UN and its role in international law with links to primary sources.
American Society for International Law - ASIL's mission is to foster the study of international law and to promote the establishment and maintenance of international relations on the basis of law and justice. Be sure to check out the Resources/Publications tab which will lead you to a Electronic Resources Guide
Cornell Law Library Legal Information Institute - has useful links to world legal materials country by country, continent by continent, the Internet-accessible sources of the constitutions, statutes, judicial opinions, and related legal material from around the globe.
Cornell Law Library International Law - good broad coverage of useful sources.
Law Library of Congress - an arm of the LOC has a good set of pointers to useful sources in international law.
WWW Virtual Library: International Affairs Resources - very broad coverage of all things international