At last month's Together for the Gospel conference, C.J. Mahaney mentioned that David Powlison's article titled God's Grace and Your Sufferings is the single finest essay he's ever read on the subject of suffering.
I had read the article before, but recently I've been re-reading it. Mahaney is right, it is a wonderful essay. After reading it, I don't think you'll ever sing the hymn How Firm a Foundation the same way (the essay is basically an extended meditation on that great hymn).
You can read the article online here (Powlison's article begins on page 145).