Here are the number of citations of authorities found in Secunda pars in the Summa theologiae of St. Thomas Aquinas. Obviously, St. Augustine and Aristotle are the most prevalent.
Gregory the Great 439
John Damascene 168
Isidore of Seville 120
Roman Law 102
Gregory of Nyssa (actually Nemesius of Ephesus) 41
Prosper of Aquitaine 19
Hilary of Poiteiers 12
These are based on Busa's concordance and lifted from Servais-Theodore Pinkaers, OP "The Sources of the Ethics of St. Thomas Aquinas" in The Ethics of Aquinas, Stephen J. Pope, ed. (Georgetown University Press: Washington DC, 2002), 17.