Encyclopedia of early Christianity. Ed. by Everett Ferguson. Garland Pub., 1997. Designed for the non-specialist, this work covers the period from the life of Jesus to about A.D. 600. Subjects include persons, places, doctrines, practices, art, liturgy, heresies, and schisms.
Bibliographies attached include primary and secondary sources.
Encyclopedia of the early church. Produced by the Institutum Patristicum Augustinianum and edited by Angelo Di Berardino. Oxford University Press, 1992. Hillerbrand, Hans Joachim. Historical dictionary of the Reformation and Counter-Reformation.