Reddit mentions of Predestination and Justification: Two Theological Loci (Sixteenth Century Essays and Studies, V.68)

I'd recommend against Barth's Church Dogmatics unless you are quite well versed in theology, and like reading long and sometimes confusing sentences.

Interested in Church Fathers?

Oden's Classical Christianity is pretty decent. It tries to break down the typical "systematic theology" headings using the early church (and some later ones). Not perfect, but there isn't one I've read yet that beats it.

Augustine's Confessions is a must if you haven't read it yet. Its autobiographical yet very spiritual and insightful at the same time.

Chrysostom's On the Priesthood is a great writing that can apply to anyone, not just those seeking ordination.

Athanasius' On the Incarnation focuses on the person of Christ, and what it meant for God to become man.

Basil's On the Holy Spirit is a great exposition on not just how the Holy Spirit is argued to be part of the Trinity, but also Christ. Very great reading for people questioning it or curious about it.

Reformation Fathers?

Peter Martyr Vermigli's Predestination and Justification is great. John Calvin in a letter said Vermigli had a better understanding of Predestination than he did, which is funny since Calvin is known for predestination today.

Martin Luther's Theological Works has most of his important works, including Bondage of the Will.

Richard Muller's Post-Reformation Reformed Dogmatics, 4 vol. but try not to pay $325 for it. Its out of print so might be a bit hard to find for a reasonable price. If you are able to find it though, it's a gold mine. Also check out other of his books.

More contemporary?

Abraham Kuyper's Lectures on Calvinism is a classic on the Reformed faith.

Herman Bavinck's Abridged Reformed Dogmatics is great, and in my opinion one of the best Systematic Theologies available. More of a Dutch Reformed than Presby bent, but essentially the same.

Karl Barth's Dogmatics in Outline is a very abridged version of Church Dogmatics, and would recommend it over the original source unless you have a lot of free time or want to be a Barth scholar.

Thats what I can think of off the top of my head. If you have other specific ones I can find other stuff.