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 illustration)
Art & Architecture
Warburg Institute Iconographic Database
The Chapel of Saints Primus and Felicianus in the church of Santo Stefano Rotondo in Rome (gallery of photos of the church, including the mosaics in the chapel, photo of the apse mosaic)
Post-Biblical Saints Art Index
Emblems of Saints by Which They Are Distinguished in Works of Art by F. C. Husenbeth.
Nihil sub sole novum 