Tony Jones is a Christian theologian and he has started a series in which he tackles the toughest arguments against Christianity:
… this series is for everyone who doubts. It’s for your friends who are agnostic and atheistic. It’s a place for them to email me a question, and get an honest answer — even if the answer doesn’t necessarily show Christianity in the best light. It’s a place for you to submit the biggest hurdle you have to fully giving yourself over to the Christian faith.
All the details on submitting your questions are here. Challenge him! Make him sweat!