I have been asked quite a few times recently what to read to begin studying the Church fathers. These are a few of the resources that helped me begin to study Patristic theology.
First, I must recommend two essential volumes. One is J.N.D. Kelly's Early Christian Doctrines, and the other is Jeraslov Pelikan's The Christian Tradition vol. 1: The Emergence of the Catholic Tradition. These are really the two standard scholarly introductions to Patristic theology. While I don't always agree, the extensive one volume treatment of such a broad topic remains unsurpassed.
I do not recommend reading the Ancient Christian Commentaries series, nor do I recommend Jurgen's three volume introduction to the fathers. These are commonly recommended resources that I have found less than helpful. Regarding the Ancient Christian Commentary series, I have found that the quotes are selective, and contain no context. A list of Patristic citations often betrays the author's beliefs rather than the father who is being quoted. I also find it somewhat strange that these volumes contain quotes from known heretics such as Pelagius. Jurgen's volumes betray a heavy Roman Catholic bias. The quotes he selects show continuity with later defined Roman Dogmas which are often far from the majority views in the early Christian period.
Rather than reading compilations of Patristic quotes, I would recommend going to the sources themselves. But where should one begin? There are so many volumes out there, it is just about impossible to read them all. I will give you some of my personal favorites, though there is far more out there, and I'm sure others would list different books than I will recommend.
First, I recommend Augustine's Confessions. This is an easy to read (provided you get a modern translation) autobiography that contains numerous great spiritual insights. Most people I have met who have an interest in Patristics began with this book, including myself. Second I recommend reading the apostolic fathers. I would recommend Michael Holmes translation, as a modern English version. This contains the earliest Christian writings. While you may be flat out confused by the Shephard of Hermas, the epistle of I Clement, the Ignatian writings, and the epistle to Diognetus are spiritual gems.
And on to my personal favorites:
Irenaues's On the Apostolic Preaching This is a great introduction to the Christian faith from one of the greatest early Christian writers. http://www.amazon.com/Apostolic-Preaching-Irenaeus-Saint-Bishop/dp/0881411744/ref=sr_1_1?ie=UTF8&qid=1321984147&sr=8-1
Augustine's On the Spirit and the Letter This was one of Luther's favorite writings, as it introduced him to what would be known as the distinction between law and gospel. This can be found in a modern translation in http://www.amazon.com/Answer-Pelagians-Works-Saint-Augustine/dp/1565480929/ref=sr_1_10?ie=UTF8&qid=1321984376&sr=8-10
Prosper of Aquitaine's The Call of All Nations. This book is quoted in the Augsburg Confession (though attributed to Ambrose) and was often recommended by Luther. It is by far the best book written on the subject of grace and predestination in the first 1500 years of the church. Prosper defends a moderate Augustinianism which defends both the election of grace, and God's universal saving will. http://www.amazon.com/14-St-Prosper-Aquitaine-Christian/dp/0809102536/ref=sr_1_1?s=books&ie=UTF8&qid=1321984612&sr=1-1
Ambrose's Patriarchal Treatises, specificall On Jacob and the Happy Life. Ambrose is a brilliant rhetorician, and while often his exegesis is strained, his Christ centered pastoral approach brings out some of the best preaching the church has ever seen. http://www.amazon.com/Seven-Exegetical-Fathers-Church-Paperback/dp/081321355X/ref=sr_1_2?s=books&ie=UTF8&qid=1321984807&sr=1-2
Finally, so as not to be too overwhelming in my recommendations, I recommend John Chrysostom's Commentary on Galatians. Chrysostom's commentaries follow a grammatical historical approach, much like a modern commentary would. This is a work I have continually come back to for edification and encouragement in my Christian life. This can be found with some of his other excellent commentaries. http://www.amazon.com/NICENE-POST-NICENE-FATHERS-St-Chrysostom-Thessalonians/dp/1602066140/ref=sr_1_6?s=books&ie=UTF8&qid=1321985027&sr=1-6
Let me know if this is helpful, or recommend other introductory resources that I may not have come across that you have found useful in Patristic study.