Argos
-- a search engine for sites devoted to ancient & medieval culture
http://argos.evansville.edu/

The Classics and Mediterranean Archeology Home Page
-- a huge index of classical websites
http://classics.lsa.umich.edu

Diotima: Materials for the Study of Women and Gender in the Ancient World
-- articles, bibliographies, texts in translation, etc.
http://www.uky.edu/ArtsSciences/Classics/gender.html

On-Line Reference for Medieval Studies
-- a large collection of medieval texts and resources
http://orb.rhodes.edu/default.html

And, for specific authors:

Virgil
http://ccat.sas.upenn.edu/~joef/vergil/home.html

Augustine
http://ccat.sas.upenn.edu/jod/augustine.html

Marie de France
http//:www.fln.vcu.edu/mdf/mdf.html

Thomas Aquinas
http://www.ktu.ruu.nl/thomas/