You can use the date operator to browse public domain books in Google Books. I’m not entirely sure why the covers of some of these books remain under copyright. Any ideas? I’ve also noticed a few scanning errors and some pretty neat finds like this one which gives the name of every librarian in the US and Canada working in a library holding over 1,000 volumes. Google Books clearly uses keyword indexing to make these books searchable. How great would it be to have this one in a database? You can see a few images that I particularly liked over at Flickr.