Here are some web sites to start your research:
The Index of Christian Art - this is the premier resource for the study of medieval iconography and includes over 200 images of paintings by Giotto.
International Center of Medieval Art - This organization publishes a newsletter and is based at the Cloisters in New York city. There are related links to medieval texts, early Christian documents and manuscripts.
Labyrinth: A World Wide Web Server for Medieval Studies, sponsored by Georgetown Univerisity.
Manuscript Resources - The largest database devoted to medieval manuscripts
Spanish Medieval Monasteries in Guadalajara - photographs and more!
Studies in Western Tapestry - aims to promote collaboration and the exchange of expertise on western tapestry produced between 1400 - 1960.
Byzantium: The Byzantine Studies Page
Byzantine Studies Bibliography
The Glory of Byzantium - The Metropolitan Museum of Art's on-line exploration of Byzantium was created in conjunction with the international loan exhibition The Glory of Byzantium This on-line exploration moves beyond the time frame of the exhibition and includes examples of art from the first golden age of Byzantine art (324-730) and the late period, which ended with the Turkish conquest in 1453.
Bibliography on Women in Byzantium lists primary and secondary sources available in translation, compiled by Thalia Gouma-Peterson, Wooster College.