The Valley of Vision by an Unknown Puritan.
This is a certified Christian classic, a collection of Puritan prayers, that for reasons I cannot fathom, has not been digitized yet by Project Gutenberg or CCEL or anyone else. As it's in public domain you'd think it would be a no-brainer.
It would make a great devotional for Logos, and a resource I believe preachers would like to have for sermon prep.