Ron Unz, a long-time Wikimedia supporter, alerted me to this personal project that he's been working on for a long time:
It's an archive of periodicals, books, and videos, some of which hosted there, some externally.
Examples:
http://www.unz.org/Publication/SaturdayRev http://www.unz.org/Publication/Century
Timeslice from the outbreak of WWI:
http://www.unz.org/Publication/AllArticles?Period=1914aug
According to Ron, the system contains almost 400,000 authors and their writings. A couple of examples of author pages:
http://www.unz.org/Author/MenckenHL http://www.unz.org/Author/WhartonEdith
Ron believes that the copyright situation is clear -- that either it's PD due to age, due to lack of copyright renewal, or that he has permission in some cases via licensing agreements. In any case, there's quite a bit of unambiguously public domain stuff there that I haven't seen digitized elsewhere, and it should be useful as a research library for Wikipedians as well.
Cheers, Erik