In no particular order and leaving off books already mentioned (e.g. 1984, Siddartha, which would have been on my list). I tried to make this rather varied, but it was hard.
Stranger in a Strange Land - Robert Heinlein
Stranger in a Strange Land, winner of the 1962 Hugo Award, is the story of Valentine Michael Smith, born during, and the only survivor of, the first manned mission to Mars. Michael is raised by Martians, and he arrives on Earth as a true innocent: he has never seen a woman and has no knowledge of Earth's cultures or religions. But he brings turmoil with him, as he is the legal heir to an enormous financial empire, not to mention de facto owner of the planet Mars. With the irascible popular author Jubal Harshaw to protect him, Michael explores human morality and the meanings of love. He founds his own church, preaching free love and disseminating the psychic talents taught him by the Martians. Ultimately, he confronts the fate reserved for all messiahs.
Band of Brothers - Stephen Ambrose
As good a rifle company as any in the world, Easy Company, 506th Airborne Division, U.S. Army, kept getting the tough assignments -- responsible for everything from parachuting into France early D-Day morning to the capture of Hitler's Eagle's Nest at Berchtesgaden. In "Band of Brothers," Ambrose tells of the men in this brave unit who fought, went hungry, froze, and died, a company that took 150 percent casualties and considered the Purple Heart a badge of office. Drawing on hours of interviews with survivors as well as the soldiers' journals and letters, Stephen Ambrose recounts the stories, often in the men's own words, of these American heroes.
Isaac Asimov: The Complete Stories, Vol. 1 (which includes the story "The Last Question" which was supposedly Asimov's favorite of his own stories). Here is the opening line:
The last question was asked for the first time, half in jest, on May 21, 2061, at a time when humanity first stepped into the light. The question came about as a result of a five dollar bet over highballs, and it happened this way ...
Malazan Book of the Fallen - series by Steven Erikson (multiple novels). Synposis of the first book, Gardens of the Moon:
The Malazan Empire simmers with discontent, bled dry by interminable warfare, bitter infighting and bloody confrontations with ancient and implacable sorcerers. Even the imperial legions, long inured to the bloodshed, yearn for some respite. Yet Empress Laseen's rule remains absolute, enforced by her dread Claw assassins.
For Sergeant Whiskeyjack and his squad of Bridgeburners, and for Tattersail, their lone surviving mage, the aftermath of the siege of Pale should have been a time to mourn the many dead. But Darujhistan, last of the Free Cities, yet holds out. It is to this ancient citadel that Laseen turns her predatory gaze.
However, the Empire is not alone in this great game. Sinister, shadowbound forces are gathering as the gods themselves prepare to play their hand . . .
Conceived and written on a panoramic scale, Gardens of the Moon is epic fantasy of the highest order--an enthralling adventure by an outstanding voice.
The Count of Monte Cristo - Alexandre Duma
I sincerely hope no synopsis is needed. This is my favorite "classic" book.