What are the other four? I'm begging!
The Count of Monte Cristo (Dumas) has to rank right up there. Even the unabridged version is nearly impossible to put down.
For 20th Century literature, Invisible Man and Brideshead Revisited are among my favorites. I also have a weakness for Tolkien-- I re-read Lord of the Rings every 4 or 5 years.
For modern fiction, I love almost anything by Richard Russo (Empire Falls, Nobody's Fool, The Risk Pool).
All the King's Men, however, stands in a special class. I think you just talked me into taking it off my bookshelf! (I do need SOMETHING to take my mind off all these polls for the next 10 days.)