This is a 4:48 video clip in which Greg Koukl recommends the following books:
Mere Christianity by C. S. Lewis
I Don’t Have Enough Faith to Be an Atheist by Norman Geisler and Frank Turek
The Case for Christ by Lee Strobel (and Strobel’s related titles)
Scaling the Secular City by J. P. Moreland
Reasonable Faith by William Lane Craig
Thinking About God by Greg Ganssle
The first three books are more popular and the second three more philosophical (yet still accessible).
Be sure to see the video at Stand to Reason to get Greg’s color on each book.