The Ecole Glossary: Contains topics relating to Early Church History, including many medieval philosophers.
On God's Existence: from the Medieval Sourcebook.
St. Thomas Aquinas and Medieval Philosophy: Article covering from Abelard and Anselm to Aquinas and the Summa, written by D.J. Kennedy, O.P.
St. Thomas Aquinas: From the Catholic Encyclopedia, New Advent Online.
The Summa Theologica: Excerpts from the Catholic Encyclopedia, New Advent Online.
William of Ockham: Biography and main points of his philosophy.