Vast archive of social science data for use with statistical software such as SAS, SPSS, Stata and R. 1962 to present.
When you find awesome data elsewhere, try to find its original source. Github or Kaggle might be where you find it, but it might have been manipulated before it was posted there. Follow the trail back to get to the source, the most raw form of the data, and where the documentation from the data gatherer might be located!