On his Answering Islam blog, Sam Shamoun, based on the work of William Albrecht, has produced a series of quotes from early Christians attesting to the post-partum virginity of Mary:
Church Father's on Mary's Perpetual Virginity
While some come from questionable sources, such as the Protoevangelium of James, it is a decent collection of quotes, though it is missing a few. Here are two authors of the early patristic age who should be added to this list by Sam:
Hegesippus
The notion that the brothers of Jesus were in fact something other than true siblings developed over time in the post-apostolic church . . . The second-century writer, Hegesippus [mentioned] James “the brother [αδελφος] of the Lord,” (Ecclesiastical History, 2.23) and Jude “who is said to have been the Lord’s brother [αδελφος] according to the flesh,”(Ibid., 3.22) as well as Simeon the son of Clopas whom Hegesippus calls “the cousin [ανεψιος] of the Lord.”(Ibid., 4.22) The fact that Hegesippus knows a distinction between these two relationships indicates that when he uses αδελφος he does with biological siblings in mind. (Eric D. Svendsen, Who is My Mother? The Role and Status of the Mother of Jesus in the New Testament and Roman Catholicism [Amityville, N.Y.: Calvary Press, 2001], 99)
Irenaeus of Lyons
Irenaeus of Lyons (130-202) did not hold to the perpetual virginity of Mary as a doctrine (let alone a dogma) but seems to have rejected the postpartum virginity of Mary. In Against Heresies 3.21.10 we read (emphasis added):
For as by one man's disobedience sin entered, and death obtained [a place] through sin; so also by the obedience of one man, righteousness having been introduced, shall cause life to fructify in those persons who in times past were dead. And as the protoplast himself Adam, had his substance from untilled and as yet virgin soil ("for God had not yet sent rain, and man had not tilled the ground"), and was formed by the hand of God, that is, by the Word of God, for "all things were made by Him," and the Lord took dust from the earth and formed man; so did He who is the Word, recapitulating Adam in Himself, rightly receive a birth, enabling Him to gather up Adam [into Himself], from Mary, who was as yet a virgin.
The phrases italicised (“as yet [a] virgin”) are clearly intended by Irenaeus to be taken as parallel to one another. Just as the soil of the earth was as yet a virgin (but only until shortly after when it was tilled), so also Mary was as yet a virgin before giving birth to Jesus. The direct implication is that she did not remain a virgin thereafter. While not explicit, it does show, at the very least, that the perpetual virginity of Mary was a doctrine unknown to Irenaeus.
For a more thorough analysis of Mariology, see my book-length treatment: