The reality of evil has sometimes been labeled "the Achilles heel of Christianity" because, as the argument goes, how can evil exist if God is both good and sovereign? In lieu of evil's presence, the skeptic says, either God is good but not sovereign or He is sovereign but not good. Unfortunately, people who argue this way have little to no understanding of biblical redemption. In fact, Christianity shines the brightest when it addresses the reality and cure for evil.
NT Wright's Evil and the Justic of God is the best book I've ever read on the problem of evil. Here's a little blurb from the DVD based on the book:
Evil, Redemption, and NT Wright
"Evil and the Justice of God"
An N.T. Wright Book Recommendation