I really like Catherine Breyter who does the About.com page on Alternative Religions. Here she has a short article on "Why do people suffer?", and names it as one of the religious questions that is hardest to deal with. I think she is so right about that, I think it turns a lot of people away from religion.
I'm very fond of the writings of the Biblical scholar Bart Ehrman, and he wrote a book on this topic - God's Problem - How the Bible Fails to Answer Our Most Important Question - Why We Suffer. He does his best to answer the question, and in the end finds it unanswerable, and leaves Christianity to become an agnostic over it. But he does, in my mind, a very thorough job of investigating the question.