Perseus Digital Library
The Perseus Digital Library has made available online a collection covering the history, literature and culture of the Greco-Roman world.
Corpus Scriptorum Latinorum
Online texts from Augustine to Vergil, sorted by author and including links to Latin, English, and foreign language translations.
LacusCurtius: Into the Roman World
A major site on Roman antiquity. Contains a number of primary sources as well as a gazetteer and a number of secondary works.
The Patrologiae Latina (Series Latina) offers influential works of late ancient and early medieval theology, philosophy, history, and literature. The Patrologia Latina Database (PLD) contains 221 volumes and represents a complete electronic version of the first edition of Jacques-Paul Migne's Patrologia Latina (1844-1855 and 1862-1865).
Acta Sanctorum is a collection of documents examining the lives of saints, organised according to each saints feast day.