Yes, we've got ECF, and that's great. But if I want to read through Augustine's City of God for example, which is on my list of books I've yet to read that I want to someday soon, I'd rather read it in a stand-alone edition such as Penguin Classics or Modern Library. They've often got more recent translations, new introductions, and usually extensive footnotes. Also it would be stand-alone so I could tag it as "FINISHED" once I've read it, even if I haven't read the other works of his that come in that ECF volume.
If I go into the Regent College Bookstore, they've got a whole huge bookcase of Christian classics (we're talking Early Church Fathers and that level of "classic"ness) in print, and it's like being a kid in a candy store. I would love to see that experience replicated in the Logos catalog.
Wish I could post a list of suggested titles right now but they are in the middle of revamping their website and their catalog is offline at the moment.
However, start with Augustine (based on my print library and what I can find on Amazon.com):