For international due diligence and investigative research, I’ve found Investigative Dashboard to be a wonderful resource:
Investigative Dashboard (ID) has been developed by the Organized Crime and Corruption Reporting Project (OCCRP), the world’s leading cross border investigative reporting organization. OCCRP designed Investigative Dashboard as a transnational collaborative effort to help journalists and civil society researchers expose organized crime and corruption around the world. It hosts three core tools: a crowd-sourced database of information and documents on persons of interest and their business connections, a worldwide list of online databases and business registries, and a research desk where journalists can go for help in sourcing hard to find information.
The collection of business registries and related databases is terrifically useful.