This is a list from europa.eu, the official website of the European Union. It contains information about traineeship programs with EU institutions including the Commitee of the Regions, the Council of the European Union, the Court of Justice of the European Union, the European Central Bank, the European Commission, the European Court of Auditors, the European Economic and Social Commitee, the European External Action Service, the European Investment Bank, the European Ombudsman and the European Parliament.
You can use this resource to get a quick idea of the range of formal traineeships offered by EU institutions, including information about eligibility and duration of speficic traineeships. Additionally, the resource contains links to detailed descriptions of each program.