Several on-line Databases contain digitized medieval texts :
UAN-ALIM (Latin texts)
http://www.uan.it/alim/letteratura.nsf/Homepage!OpenForm
al-Waraq et al-Maktaba al-Shamela (arab)
http://www.alwaraq.net
http://shamela.ws/
Parnaseo (Spanish texts) : http://parnaseo.uv.es/memorabilia.htm
Perseus (Latin and Greek texts) : http://www.perseus.tufts.edu/
