ESV Online – The English Standard Version with accompanying study tools.
The Bible Gateway – A valuable Bible search tool.
The Westminster Standards including the Confession of Faith, Larger Catechism, and Shorter Catechism with Scripture proofs.
Institues of the Christian Religions by John Calvin
Economy of the Covenants Between God and Man by Herman Witsius
The Doctrine of the Covenant in Reformed Theology by Geerhardus Vos
A One-Year Bible Reading Calendar
The Red Trinity Hymnal - The revised version used by most OPC congregations.
The Blue Trinity Hymnal – includes lyrics, tunes, etc.
Commentary on the Westminster Confession of Faith by A.A. Hodge
Commentary on the Westminster Confession of Faith by Robert Shaw