Books
There are tons of great books written about the topics below. I've tried to simplify the list so it's not too overwhelming!
Basic Apologetics:
Mere Christianity, C.S. Lewis
I Don't Have Enough Faith To Be An Atheist, Norman Geisler & Frank Turek
Stealing From God, Frank Turek
Cold Case Christianity, J. Warner Wallace
Case For Christ, Lee Strobel
The Case For the Resurrection of Jesus, Gary Habermas & Michael Licona
Tactics, Greg Koukl
Apologetics and Theology for Parents and Kids:
How Do We Know God Is Really There?, Melissa Cain Travis
How Do We Know God Created Life?, Melissa Cain Travis
How Do We Know Jesus Is Alive?, Melissa Cain Travis
Cold Case Christianity for Kids: Investigate Jesus with a Real Detective, J. Warner Wallace
Keeping Your Kids on God's Side, Natasha Crain
What Is God Like? (whole series), William Lane Craig
New Testament Documents/ The Bible:
The New Testament Documents, F.F. Bruce
Unbreakable, Andrew Wilson
A General Introduction to the Bible, Norman Geisler
Fabricating Jesus: How Modern Scholars Distort the Gospels, Craig A. Evans
Philosophy/Logic:
Come Let Us Reason, Norman Geisler
The Last Superstition: A Refutation of the New Atheism, Edward Feser
Love Your God With All Your Mind, J.P. Moreland
Worldview:
Jesus Among Other Gods, Ravi Zacharias
Why Jesus?, Ravi Zacharias
Science/ Age of the Earth/ Creation/ Evolution:
Seven Days That Divide The World, John C. Lennox
God's Undertaker: Has Science Buried God?, John C. Lennox
The Edge of Evolution: The Search for the Limits of Darwinism, Michael Behe
Hidden Treasures in the Book of Job: How the Oldest Book in the Bible Answers Today's Scientific Questions, Hugh Ross
Sexual Ethics:
The Secret Thoughts of an Unlikely Convert, Rosaria Champagne Butterfield
What Does the Bible Really Teach About Homosexuality?, Kevin DeYoung
Is God Anti-Gay?, Sam Alberry
Islam:
Seeking Allah, Finding Jesus: A Devout Muslim Encounters Christianity, Nabeel Qureshi
Devotional/Christian Living:
Confessions, St. Augustine
The Cost of Discipleship, Dietrich Bonhoeffer
The Pursuit of God, A.W. Tozer
Voice of A Prophet: Who Speaks for God? A.W. Tozer
Knowing God, J.I. Packer
The Call, Os Guinness
The Insanity of God, Nik Ripken
Orthodoxy, G.K. Chesterton
Bible Study:
Encountering The Old Testament, Bill T. Arnold
Encountering the New Testament, Walter A. Ewell
(I have found all the "Encountering Biblical Studies" books to be very helpful!)
Against The Flow: The Inspiration of Daniel in an Age of Relativism, John C. Lennox
Other Great Resources:
Kingdom of the Cults, Walter Martin
Is God A Moral Monster?: Making Sense of the Old Testament God, Paul Copan
Apologetics Study Bible, Holman Bible Staff