What are some good datasets for Data Science and Machine Learning?

A dataset is a collection of data, usually presented in tabular form. Good datasets for Data Science and Machine Learning are typically those that are well-structured (easy to read and understand) and large enough to provide enough data points to train a model. The best datasets are often those that are open and freely available – such as the popular Iris dataset. However, there are also many commercial datasets available for purchase. In general, good datasets for Data Science and Machine Learning should be:
– Well-structured
– Large enough to provide enough data points
– Open and freely available whenever possible