I totally agree with Marisol Herrera-Rivero and Rashidul Hasan Hridoy. Kaggle is a great place to start with different types of datasets. If you have a particular domain of interest as well as good domain knowledge, you can simply search the web for certain keywords to find specific repositories. Thanks
Marisol Herrera-Rivero Im looking for MRI dataset for deep learning (it would be grate when it was already preprosessed), and also CSV data with MS biomarkers for tradicional ML techinques