Joseph Priestley. “The theological and miscellaneous works of Joseph Priestley Written in English edited with notes by John Towill Rutt. Published 1817 by Printed by G. Smallfield in London.” is a must read! 

NOTE: Joseph Priestley was a Unitarian, meaning he didn't believe in the Pre-Human existence of Jesus Christ. But he certainly did not believe in the Tri{3}nity and did some fine research on the history and doctrines of the early Christian Congregation. 

I highly recommend:

Vol 6 “Containing An History Of Early Opinions Concerning Jesus Christ!”

NOTE: The second link above takes you to the very start of the volume and in the first few chapters he disagrees with the doctrine of Jesus Pre-Existence. So the first link by-passes those chapters and goes to the part about the ANF or "Apostolic Fathers" etc.

A list of links to his other works online at Wikipedia: