Since the ECFs who thought the rock was Peter's confession were already mentioned in this thread.. I'll mention the ones who understood the rock to be Peter.. so that we have both sides represented.
http://www.davidmacd.com/catholic/pope_peter_rock.htm
Tatian the Syrian (170 A.D.)
"Simon Kephas answered and said, 'You are the Messiah, the Son of the living God.' Jesus answered and said unto him, 'Blessed are you, Simon son of Jonah: flesh and blood has not revealed it unto thee, but my Father which is in heaven. And I say unto thee also, that you are Kephas, and on this Rock will I build my Church; and the gates of hades shall not prevail against it" (The Diatesseron 23 [A.D. 170]).
Tertullian (220 A.D.):
"Was anything hid from Peter, who was called the Rock, whereon the Church was built; who obtained the keys of the Kingdom of Heaven, and the power of loosing and of binding in heaven and on earth?" (Tertullian, De Praescript Haeret).
Tertullian thereafter writes to criticize Pope Callistus I by saying ....
"I now inquire into your opinions, to see whence you usurp the right for the Church. Do you presume, because the Lord said to Peter, 'On this rock I will build my Church ...[Matt 16-19]' that the power of binding and loosing has thereby been handed over to you, that is, to every church akin to Peter? What kind of man are you, subverting and changing what was the manifest intent of the Lord when He conferred this ***personally on Peter****? 'On you,' He says, 'I will build my Church; and I give to you the keys'...." (Tertullian, On Modesty 21:9-10)
The Apocryphal Letter of St. Clement of Rome to St. James (C. 221 A.D.)
"Be it known to you, my lord, that Simon [Peter], who, for the sake of the true faith, and the most sure foundation of his doctrine, was set apart to be the foundation of the Church, and for this end was by Jesus Himself, with His truthful mouth, named Peter" (Letter of Clement to James 2 [A.D. 221])
The Clementine Homilies (C. 221)
"[Simon Peter said to Simon Magus in Rome:] For you now stand in direct opposition to me, who am a firm rock, the foundation of the Church [Matt. 16:18]" (Clementine Homilies 17:19 [A.D. 221]).
St. Hippolytus (225 A.D.):
"Peter, the Rock of the Church ..." (Hippolytus in S. Theophan, n. 9, Galland, ii. p. 494). "Peter, the Rock of the Faith, whom Christ our Lord called blessed, the teacher of the Church, the first disciple, he who has the Keys of the Kingdom." (Hippolytus, Ex Fabricio, Op. Hippol. tom. ii. De Fine Mundi et de Antichristo, n. 9).
Origen (230-250 A.D.):
"See what the Lord said to Peter, that great foundation of the Church, and most solid Rock, upon which Christ founded the Church ..." (Origen, In Exodus. Hom. v. . 4 tom. ii).
"Look at [Peter], the great foundation of the Church, that most solid of rocks, upon whom Christ built the Church [Matt. 16:18]. And what does our Lord say to him? 'Oh you of little faith,' he says, 'why do you doubt?'" [Matt. 14:31] (Homilies on Exodus 5:4 [A.D. 248]).
"Upon him (Peter), as on the earth, the Church was founded." (Origen, Ep. ad. Rom. lib. v.c. 10, tom iv.)
"Peter, upon whom is built Christ's Church, against which the gates of hell will not prevail." (Origen, T. iv. In Joan. Tom. v.)
St. Cyprian (246 A.D.):
"For first to Peter, upon whom He built the Church, and from whom He appointed and showed that unity should spring ..." (Cyprian, Ep. lxxiiii ad Fubaian).
"God is one, and Christ is one, and the Church is one, and the Chair (of Peter) is one, by the Lord's word, upon a Rock ..." (Cyprian, Ep. xl. ad Pleb).
"Peter, also to whom the Lord commends His sheep to be fed and guarded, on whom He laid the foundation of the Church ...." (Cyprian, De Habitu Virg).
St. Ephream the Syrian (350-370 A.D.):
"Simon my follower, I have made you the foundation of the Holy Church. I betimes called you Peter because you will support all its buildings. You are the inspector of those who will build on earth a Church for Me. If they should wish to build what is false, you, the foundation, will condemn them. You are the head and fountain from which all My teaching flows." (Ephraem, Homilies 4:1).
"Peter, who was called Kephas, he who was captured on the sea shore, and who received testimony from the great Shepherd, that 'Upon this Rock I will build my Church.'" (Ephraem T. iiii. Gr. De Sacred).
"That Rock which He set up that Satan might stumble thereon, Satan, on the other hand, wished to put this Rock in the way of the Lord that He might stumble upon it, when Peter said, 'Far be it from Thee, Lord.' [Matt 16:22-23] (Ephraem, Sermo de Transfig. Dom., Sec. IV).
St. Hilary of Poitiers (356 A.D.)
"Blessed Simon who, after his confession of the Mystery, was set to be the foundation-stone of the Church and received the Keys of the Kingdom." (Hilary, De Trinitate, 6:20).
"Peter, the first Confessor of the Son of God, the Foundation of the Church, ..." (Hilary, Tract in Ps. cxxxi.)
"And in truth Peter's confession obtained a worthy recompense ....Oh! in thy designation by a new name, happy Foundation of the Church, and a Rock worthy of the building up of that which was to scatter the infernal laws of the gates of hell!" (Hilary, Comm. in Matt. c. xvi.)
St. Cyril of Jerusalem (363 A.D.):
"Our Lord Jesus Christ then become man, but by the many He was not known. But wishing to teach that which was not known, having assembled His disciples, He asked, 'Who do you say that I the Son of man am?' ...And all being silent, for it was beyond man to know, Peter, the Foremost of the Apostles, the Chief Herald of the Church, not using language of his own finding, but having his mind enlightened by the Father, says unto Him, 'Thou art the Christ,' and not simply that, but, 'the Son of the living God.' And a blessing follows the speech. ....' ....and upon this Rock I will found my Church ...' " (Cyril, Catech, xi. n. 3).
"He said to Peter, 'And upon this Rock I will build my Church.' " (Cyril, Catechetical Lectures, 18:25).
Optatus (367 A.D.)
"You cannot deny that you are aware that in the city of Rome the episcopal chair was given first to Peter; the chair in which Peter sat, the same who was head - that is why he is also called Cephas ["Rock"] - of all the apostles; the one chair in which unity is maintained by all" (The Schism of the Donatists 2:2 [A.D. 367]).
St. Gregory Nazianzen (370 A.D.):
"See thou that of the disciples of Christ, all of whom were great and deserving of the choice, one is called a Rock and entrusted with the foundations of the Church." (Gregory Naz., T. i or xxxii).
"Peter, the Chief of the disciples, but he was a Rock ... (Gregory Naz., T. ii.)
"[Peter], that unbroken Rock who held the keys." (Gregory Naz., Sect. ii Poem Moral. tom. ii.)