Here's an interesting collection of yearbooks from the digital collection HathiTrust.
It's strange in that the collection links the full .pdf yearbooks directly from the catalog which I think I've only seen one time before, and it was the university's library catalog not a private digital consortia like this one. Really interesting to see the tech set up like this and that a private group is interested in preserving a yearbook as rich in college football history as this one. The copyright and watermark indicate that Google did the digitization for this set of yearbooks.
The University of Michigan has a robust collection of yearbooks available online.