I've long been a fan of Dover Books, the no-frills publisher of reissued and public-domain texts. The books are typically high quality - each book has an endpage with this text:
A DOVER EDITION DESIGNED FOR YEARS OF USE We have made every effort to make this the best book possible. Our paper is opaque, with minimal show-through; it will not discolor or become brittle with age. Pages are sewn in signatures, in the method traditionally used for the best books, and will not drop out, as often happens with paperbacks held together with glue. Books open flat for easy reference. The binding will not crack or split. This is a permanent book.
What a wonderful ethos.
What I especially appreciate is how any time I want to go deep into the history of a subject, there's bound to be a trove of Dovers that will catch me up. So when I indulged in New York City architectural history, Dover has terrific books on NY bridges, the 1939 World's Fair, and a book on the city's architectural holdouts (the recalcitrant landowners who refuse to sell to the big developer, and thus get built around with remarkable consequences - see some examples here).
What's this have to do with public health? Well, needless to say, their catalog of books on medicine and public health is a joy to peruse. They have John Hooke's Micrographia, the 1665 work that helped establish the microscope as a tool for medicine. There's Florence Nightingale's Notes on Nursing. Malthus's Essay on the Principle of Population. Henry Mayhew's great study of the London Underworld, circa 1840.
If you have a jones for history and esoteric knowledge, you could do worse than to buy a couple boxes of Dover books and spend a Sunday flipping through them.