This will continue to grow as more sources are added to the list of links:
Journal of Statistics Education: http://jse.amstat.org/jse_data_archive.htm
CAUSEweb datasets: https://www.causeweb.org/cause/material-type/datasets
UCI Machine Learning Repository: https://archive.ics.uci.edu/ml/index.php
Textbook data sources USC: http://faculty.marshall.usc.edu/gareth-james/ISL/data.html
Textbook data sources Stanford: https://web.stanford.edu/~hastie/ElemStatLearn/data.html