Kaggle
Kaggle is a Community for Machine Learning and Data Science. There are many datasets available for free. It leans towards AI/ML applications but the data can just as well be used for Data Visualisation purposes.
Kaggle also has some code-focused tutorials for Data Visualisation. See Learn Data Visualization | Kaggle
data.gov.in
Open Government Data (OGD) Platform run by the Indian government. It provides a single point of access to Datasets/Apps in open formats published by Ministries/Departments. This is great for finding India specific data.
data.gov
Similiar government website for US specific data.
Tidy Tuesday
Tidy Tuesday is a weekly social data project organized by the Data Science Learning Community. They release a dataset every Monday with a goal of providing real-world datasets so that people can learn to work with data.
P.S. They also have a Podcast!
If you find more sources for datasets do share them in the class!