International Organizations
European Union:
https://europa.eu/european-union/index_en
International Committee of the Red Cross: War & Law:
https://www.icrc.org/en/war-and-law
International Monetary Fund:
http://www.imf.org/external/index.htm
International Sea Bes Authority:
https://www.isa.org.jm/
North Atlantic Treaty Organization:
http://www.nato.int/
United Nations Commission on Human Rights:
http://www.ohchr.org
United Nations Commission on International Trade Law: http://www.uncitral.org/uncitral/en/about_us.html
United Nations International Law Commission:
http://legal.un.org/ilc/
United Nations Security Council:
http://www.un.org/en/sc/
United Nations Sustainable Development Knowledge Platform: https://sustainabledevelopment.un.org/
United Nations Treaty Collection:
https://treaties.un.org/
World Trade Organization:
https://www.wto.org/index.htm
International tribunals, courts, and settlement bodies
CURIA (case law of the European Court of Justice):
http://curia.europa.eu
Documents from the Nuremberg trials (Harvard Law School Library): http://nuremberg.law.harvard.edu/
Extraordinary Chambers in the Court of Cambodia:
https://www.eccc.gov.kh/en
HUDOC (case law of the European Court of Human Rights):
http://hudoc.echr.coe.int
Inter-American Court of Human Rights:
http://www.corteidh.or.cr/
International Centre for Settlement of Investment Disputes:
https://icsid.worldbank.org/en/
International Court of Justice:
http://www.icj-cij.org/homepage/index.php
International Criminal Court:
https://www.icc-cpi.int/
International Criminal Tribunal for Rwanda:
http://unictr.unmict.org/
International Criminal Tribunal for the former Yugoslavia:
http://www.icty.org/
International Tribunal for the Law of the Sea:
https://www.itlos.org/
Permanent Court of Arbitration:
https://pca-cpa.org/en/cases/
World Trade Organization Dispute Settlement Body cases: https://www.wto.org/english/tratop_e/dispu_e/find_dispu_cases_e.htm#results
Legal blogs
American Society of International Law Blog:
https://www.asil.org/ilib
American Society of International Law Insights:
https://www.asil.org/insights
An International Law Blog:
https://internationallaw.blog/
Audiovisual Library of International Law:
http://www.un.org/law/avl/ (lectures on various topics can be found here – seems quite useful to me)
Berkeley Journal of International Law Blog:
http://berkeleytravaux.com/
Beyond The Hague:
https://beyondthehague.com/
EJIL: Talk! (Blog of the European Journal of International Law):
http://www.ejiltalk.org/
ESIL Reflections (European Society of International Law):
http://www.esil-sedi.eu/node/84
International Judicial Monitor:
http://www.judicialmonitor.org/summer2016/
International Law Observer:
http://www.internationallawobserver.eu/
International Law Reporter:
http://ilreports.blogspot.dk/
IntLawGrrl:
https://ilg2.org/
Just Security:
https://www.justsecurity.org/
Lawfare Blog:
https://www.lawfareblog.com/topic/international-law-loac
Opinio Juris:
http://opiniojuris.org/ (with a list of links on the right hand side to blogs focusing more on the political approach to international relations)
The Lawyer:
https://www.thelawyer.com/ (a news source)