C.S. Lewis might be my favorite Christian thinker of all time. A former atheist, he converted to Christianity and wrote some phenomenal books, including The Chronicles of Narnia series (Should it be "the The Chronicles of Narnia" series?), Mere Christianity, God in the Dock (which I want to read), The Screwtape Letters, and more. Mere Christianity is one of the best books I have ever read.
There's just something special about his writing. Maybe it's that he was an Englishman born in the 1800's, but he's very quotable. He also is exceptionally intelligent and (unlike many Christian writers) willing (and able) to confront atheism. Most of his writing discusses Christianity from a more philosophical standpoint, rather than scientific or historical. His two most famous ideas (according to Wikipedia, anyway, but they are the two I associate with him) are the common morality of man and the inability to classify Jesus as a great teacher:
I am trying here to prevent anyone saying the really foolish thing that people often say about Him: I’m ready to accept Jesus as a great moral teacher, but I don’t accept his claim to be God. That is the one thing we must not say. A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic — on the level with the man who says he is a poached egg — or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God, or else a madman or something worse. You can shut him up for a fool, you can spit at him and kill him as a demon or you can fall at his feet and call him Lord and God, but let us not come with any patronising nonsense about his being a great human teacher. He has not left that open to us. He did not intend to.