The University of Michigan Libraries have made over 100,000 metadata records from its MBooks collection available for OAI-PMH harvesting. The records are for digitized books in the public domain.
Here's an excerpt from the announcement:
The University of Michigan Library is pleased to announce that records from our MBooks collection are available for OAI harvesting. The MBooks collection consists of materials digitized by Google in partnership with the University of Michigan.
Only records for MBooks available in the public domain are exposed. We have split these into sets containing public domain items according to U.S. copyright law, and public domain items worldwide. There are currently over 100,000 records available for harvesting. We anticipate having 1 million records available when the entire U-M collection has been digitized by Google.