III. In the unity of the Godhead there be three Persons of one substance, power, and eternity: God the Father, God the Son, and God the Holy Ghost. The Father is of none, neither begotten nor proceeding; the Son is eternally begotten of the Father; the Holy Ghost eternally proceeding from the Father and the Son.
Resources
What is the Trinity? by R. C. Sproul
The Holy Trinity by Louis Berkhof
The Unity of the Divine Essence in Three Persons Taught, in Scripture by John Calvin
On the Trinity by St. Augustine
Brief Declaration and Vindication of The Doctrine of the Trinity (eBook) by John Owen
Of God and of the Holy Trinity by Robert Shaw
Father, Son, and Holy Spirit - Each Have a Part in Saving Sinners by James Buchanan
The Biblical Doctrine of the Trinity by B. B. Warfield
The Being, Attributes and Persons of the Godhead by Francis R. Beattie
Of the Holy Trinity by the Rev. Thomas Boston
How many Persons are there in the Godhead? by John Flavel
The Trinity by Thomas Watson
More Resources on the Trinity @Monergism
Multimedia
Of God, and of the Holy Trinity (Ch.2, Sec.2-3) by Greg Bahnsen
Predestination, Providence, God's Attributes, The Trinity (MP3 Series) by Dr. Joel Beeke
The Mystery of the Trinity (Video Lecture Series) by R. C. Sproul
The Biblical Witness of the Trinity (MP3) by R. C. Sproul
Fifth-Century Anti-Trinitarian Heresies (MP3) by R. C. Sproul
One in Essence, Three in Person (MP3) by R. C. Sproul
Trinity (9-Part Video Series) by Michael Reeves
Confessing the Triune God: Retrieving the Nicene Faith for Today's Church (MP3 Lecture Series) by Dr J Ligon Duncan III, Michael Haykin, Scott Swain