Google Books can be a helpful source for re-trying a search and identifying additional books you might search for in the catalog or request by interlibrary loan.
1. Books
2. Journal Articles
3. Newspaper Articles
4. Ephemera (pamphlets, flyers, posters)
5. Statistical Datasets
6. Geographical data
7. Conference proceedings
8. Dissertations
9. Archival material
10. Websites/Blogs/Social Media
11. Movies (online and analog)
12. Oral histories
13. Music
14. Works of Art