The United Nations: The preeminent multilateral international body, founded after World War II to help avoid a repeat of that tragedy. Their website is most useful for its links to documents.
UNICEF: The United Nations Children's Fund ('I' and 'E' since removed): A UN agency devoted to children's welfare worldwide.
World Health Organization: Part of the United Nations, the World Health Organization is the most prominant health organization in the world, and works on related projects all around the globe.
Amnesty International: One of the world's most prominant human rights organizations. Has invaluable searchable documents.
Human Rights Watch: One of the world's most prominant human rights organizations. Has invaluable searchable documents.
United For Peace: A major coordinator of antiwar efforts in the United States.
International A.N.S.W.E.R.: (Act Now to Stop War and End Racism): A major coordinator of antiwar efforts in the United States and abroad.
Gush-Shalom: Translated from Hebrew as "The Peace Bloc", Gush-Shalom is a truly wonderful source of information about a conflict which is deliberately kept in a media blackout. With the primary goals of ending the occupation and installing the green line as a permanent border between states, it hosts commentary, news, and reports from the International Soldiary Movement. A must-visit site for those who oppose the occupation.