While the webinar will only explore a few tools, this page aims to give more context, and link to many resources that I've found useful while working with (investigative) reporters. I've tried to arrange them by the type of scenario in which you'd use them: trying to solve a specific data problem, or while looking for data on a particular topic.
Most information that investigative journalists handle comes in the form of text documents, like Word files, PDFs or scanned images.
There are many public listings of datasets, such as Awesome Public Datasets and the DataHub. Much of this data requires specialized processing, though, so investigatives will have to join forces with a technologist.