Modern Hagiography
Lives of the Saints by Alban Butler.
Lives of the Saints by Sabine Baring-Gould.
The Liturgical Year by Dom Guéranger.
Medieval Hagiography
The Golden Legend (and illustrations)
Art & Architecture
Catacomba dei Santi Gordiano ed Epimaco in Rome
Warburg Institute Iconographic Database
Medieval Religion Listserv – 2016 Dillon.
The Saints in Art by Joseph Maria von Radowitz.