The collection of raw data to perform data analysis in Excel depends largely on the particular use-case that the student wish to address. For example – in case of any descriptive analysis on economical data such as GDP, growth rates, repo rates, bank rates etc. the relevant governmental statistical websites are the most authentic. Other than that, there are other online sources as well to find data for analysis such as KDnuggets, Machine learning repository by UCI, the 100k datasets from MovieLens, Data mining implementation repository, Kaggle datasets etc.
All of these data can be readily imported to excel for high-end analysis & visualization.