For Beginners:

• What is Reformed Theology by RC Sproul

• Core Christianity by Michael Horton

For Intermediates:

• Everyone's a Theologian by RC Sproul

• What is Biblical Theology by James Hamilton

For Advanced:

• Pilgrim Theology by Michael Horton

• Systematic Theology by Louis Berkhof

• Biblical Theology by Geerhardus Vos

• Kingdom Prologue by Meredith Kline

• Here is MonergismBooks, a fantastic source of recommended reading material

• A big-time reading list for those thinking about majoring in Theology in college

Monergism.com! (An awesome website for Reformed primary sources)

Core Christianity (helpful articles and resources for answering basic questions)

Ligonier Ministries (more helpful articles and books)

White Horse Inn (more in-depth podcast and articles)

Reformed Forum (more advanced podcasts and articles)

Heidelblog (more advanced podcast and articles)