As i have now begun to look at my own book collection for inspiration an author who's books always seem to scream from the shelf through content and design is Irvine Welsh. Not only is he one of my favorite writers, and produced some excellent books but always has interesting imagery and clues on the front. Similar to his book titles, once you have read the book the clues seem obvious.
Another author i have looked at is George Orwell, a novelist who's supreme intelligence and social awareness led to many fantastic books, two of which are shown below. i like the way the colour scheme is identical over both covers yet adopting different content.