Fadedpage.com is a great website run by volunteers who produce excellent free downloadable online books from authors out of copyright - your one-stop shop for Biggles or Enid Blyton, for instance.
Well, they have just made available The Great Divorce by CS Lewis - which I regard as the best book I've ever read about sin, repentance, and what makes people choose Hell.
If you haven't already read TGD: why not try it?