This page offers links to digital collections of materials for teaching, learning, and research that are appropriate for faculty and student use. Many of them are OERs (open educational resources), which are teaching, learning, and research materials that are in the public domain or have been released with a license that allows for their free use.
Millikin's Library Catalog also contains many ebooks. Search in the catalog and then limit to "Format: Electronic" or "Location: CARLI eBooks or CARLI Open Access Materials OR HathiTrust eResources (public domain) OR Open Textbook Library."