After some thought, I've decided to choose The Big Sleep as my book to design a cover for. I feel like it has very strong imagery and mood to it, which should help me gather much more concepts for my final design. Gritty crime novels are also something I'm not very familiar with so I think it will not only provide a challenge, but also allow me to approach the design with an open mind.
The Penguin Complete version of the cover.
The next step for my project will be to finish reading the book and then generate some initial designs.