I just have a few suggestions for guests (theists) that I think would provide for much more interesting and stimulating conversation than people like Ergun Caner or the completely non-sensical Way of the Master guys. Here's who I'd love to hear on the show (though who knows if they would actually be willing to do it or not):
Peter L Berger
John F Haught
I think all of these guys could probably provide for some good debate/dialogue.