In most cases, the best place to find international case law is on the websites of international courts. Most international courts have a website providing access to their decisions and opinions. Below are various websites on international case law.
Hudoc (Human Rights Documentation) provides access to the case law of the European Court of Human Rights (EHRC). The database of the ECHR also contains case law information notes. Decisions, advisory opinions and lists of cases both pending and concluded of the International Court of Justice (ICJ) are published in ICJ.
International law reports
Justis.com - International Law Reports covers international law as applied in the decisions of international courts and arbitrators as well as judgments of national courts. Annotated leading cases of international criminal tribunals contains the most important decisions with comments by experts in the field of international criminal law. HeinOnline, NexisUni and Westlaw contain case law from the UK and the US.
European case law
Since 1997 case law of European Court of Justice is accessible in all EU official languages via the court's website. EUR-Lex, the European Union's legal database, contains EU case law in all EU official languages, and case law from the period before 17/06/1997. The database EUR-lex also includes references to notes relating to the decision. You can search for case law from Member States of the European Union (EU) via the European e-Justice Portal. By selecting one of the flags listed on the right hand side you will be redirected to the relevant national page.