Ah yes, this is the classic go-to place for machine learning data sets. I implemented my first ML models using these files, especially the famous iris data set[1] which is a good one for beginners. It was so exciting to see my first multi-layer perceptron working (and to compare its results to the simple perceptron or decision tree, etc, on the same data).

[1]: http://archive.ics.uci.edu/ml/datasets/Iris