Lonesome Dove. This novel is nothing short of amazing, and the miniseries based on it got it all wrong. It is a deconstruction of the myth of the romantic old west, as dark and full of humor as any King novel. I heartily recommend it, and I envy anyone who hasn't discovered it yet.

Watchmen - there is a reason this book won the Hugo, in spite of being in graphic novel format.

Heart Shaped Box - great first novel by King's son. I'm sure it has to have been mentioned here before.

Gates of Fire - Fictionalized account of the battle of thermopylae, much much better than the awful movie 300. It will make you want to be a Spartan, even if you're an old peacenik hippy like myself.

Killer Angels - Very interesting account of the battle of Gettysburg, devastating in its protrayal of RE Lee. Its required reading at the War College, and for good reason.