Modern Hagiography
Lives of the Saints by Alban Butler.
Lives of the Saints by Francis Weninger.
Lives of the Saints by Sabine Baring-Gould.
Victories of the Martyrs by Saint Alphonsus Liguori.
Medieval Hagiography
Prudentius, Peristephanon (?)
The Golden Legend (and illustrations)
Art & Architecture
Saint Hippolyte Triptych by Dieric Bouts
Warburg Institute Iconographic Database
Guide to Christian Iconography: Images, Symbols, and Texts
Post-Biblical Saints Art Index
Sacred and Legendary Art volume II by Mrs. Jameson.
A Handbook of Christian Symbols and Stories of the Saints as Illustrated in Art by Clara Erskine Clement.
Saints and their Symbols: A Companion in the Churches and Picture Galleries of Europe by E. A. Greene.
The Saints in Art by Joseph Maria von Radowitz.
Emblems of Saints by Which They Are Distinguished in Works of Art by F. C. Husenbeth.