In no particular order:
The Decline and Fall of the Roman Empire by Edward Gibbon. Yes, this is the abridged version; I wish I had the time to read all six volumes, but unfortunately, I've yet to find a safe way to clone myself. Alas.
Three Cups of Tea by Greg Mortenson. I've had this book on my shelf for a year now, always meaning to pick it up.
Nothing But Red.
I'm not sure what the fifth book will be. I'm reading a couple now that would qualify (The Western Canon, The Well-Educated Mind, The Meaning of Sunglasses, and The Child That Books Built), but maybe I should keep this last spot "open," in case something else comes along.