Dataset Search. It spent 2019 in beta. Last week it lost beta label and is now widely available to anyone who wants to use it. In a recent blog post Dan Russell explained a couple of the features of Dataset Search and highlighted four examples of datasets that you can find through Dataset Search.
Google's Dataset Search is designed to help users locate publicly available datasets. Through the Dataset Search tool you can find datasets in the forms of Excel and CSV files, Google Earth files, zip files of images, and collections of documents. In the following video that I recorded last spring I provide an overview of how to use Dataset Search.
On a related note, Dan Russell's book The Joy of Search is a fantastic resource for learning advanced search techniques.