http://www.newadvent.org/fathers/index.html
This site has almost all of the writings of the early church father. I happened to find it by searching the book written by John Chrysostom, on the Priesthood. Before I read books about the Church history, I never had any interests in Church Fathers and did not know their significance. But as I learn more it was very insightful to find that what I know today is mostly based on the foundation of the early church fathers. Take a look at some of their writings and you will find the relevance of the writing almost around 2000 years ago. John Chrysostom, was one of the best preacher in his days. If you think that Tim Keller is your favorite speaker. I would think that Chrysostom might have been even more genius. His book, on the Priesthood, is the most classic teaching about being pastor, minister or any kinds of priest.
I like the writings of St. Augustine. Since I prefer paper I have some books of Augustine. One of favorite book of Augustine is the homilies on the first letter of John, Love One Another, Friend. I think it is amazing to see that the writings almost around 1600 years old still sound very relevant to the life today. His preaching style is very application oriented. He usually starts with questions and build a relevance between the problems of our daily life and the words of God. And then start explaining what the word of God actually means in a certain circumstances.In this sense his sermon is very apologetic. Today many sermons try to appeal to just faith only, which sometimes leads to fideism. But Augustine’s approach was not just asking to believe, but to find the truth. If you finished reading of St. Paul’s letter, I would recommend to read Augustine. He is the most significant person in Christian history right next to the Apostle Paul. We can’t miss him. You have to read him.