I've always recommended Lee Strobel's
A Case for Christ to those seeking to read a strong case for the authenticity of the Gospels. It's a great, interesting read, and it goes quickly. He also has
A Case for Faith and
A Case for a Creator, both of which I need to read. I have C.S. Lewis's
Mere Christianity, but I haven't read that yet either. I was just over half way through
A Purpose-Driven Life the last time I put it down (sadly, you will get the best results by reading a chapter a day, as the book suggests). It's an excellent book for anyone who asks the question, "why am I here?"
Lee Strobel's testimony is good, because he was once on the other side of the debate and was trying to disprove the legitimacy of the Bible when he came to believe.
Perhaps this one's not directly related, but I found
A Muslim and a Christian in Dialogue to be very interesting. It's also a fast read, and it shows the contrasts between Islam and Christianity in a friendly discussion between religious leaders of each respective religion. Many people wonder if Muslims and Christians pray to the same God, and this book should answer that question.