As I am writing this, I was about to include Childhood's End by Arthur C. Clarke, but I notice that it did not win the Hugo when it was published. I found it to be one of the more disturbing and memorable of the books I have read recently and I picked it up thinking it must have won the Hugo based on all the acclaim it has received over the years. I believe I have read that the Hugo wasn't given out the year it was published (1953) although it was nominated for a Retro Hugo in 2004...it didn't win!
The original three Foundation books by Isaac Asimov...didn't win the Hugo! But I read them knowing they were part and parcel of a science fiction readers lexicon.
What books have you read that you thought had won the Hugo or other awards but hadn't? Or what books do you think should have been nominated?