Here, via Pharyngula, then Paul Little, is a list of the "Most Significant SF & Fantasy Books of the Last 50 Years" first issued by the Science Fiction Book Club. Put the ones you've read in bold. My list is below. I've adopted Paul's convention of bolding those I have read, italicizing the ones I ought to read and striking through the ones I'm not likely to ever read. Leave a comment how this shapes up with your reading experience.
The Lord of the Rings, J.R.R. Tolkien
The Foundation Trilogy, Isaac Asimov
Dune, Frank Herbert
Stranger in a Strange Land, Robert A. Heinlein
A Wizard of Earthsea, Ursula K. Le Guin
Neuromancer, William Gibson
Childhood's End, Arthur C. Clarke
Do Androids Dream of Electric Sheep?, Philip K. Dick
The Mists of Avalon, Marion Zimmer Bradley
Fahrenheit 451, Ray Bradbury
The Book of the New Sun, Gene Wolfe
A Canticle for Leibowitz, Walter M. Miller, Jr.
The Caves of Steel, Isaac Asimov
Children of the Atom, Wilmar Shiras
Cities in Flight, James Blish
The Colour of Magic, Terry Pratchett
Dangerous Visions, edited by Harlan Ellison
Deathbird Stories, Harlan Ellison
The Demolished Man, Alfred Bester
Dhalgren, Samuel R. Delany
Dragonflight, Anne McCaffrey
Ender's Game, Orson Scott Card
The First Chronicles of Thomas Covenant the Unbeliever, Stephen R. Donaldson
The Forever War, Joe Haldeman
Gateway, Frederik Pohl
Harry Potter and the Philosopher's Stone, J.K. Rowling [But I am currently reading the Order of the Phoenix and the Half-Blood Prince awaits the completion of Phoenix]
The Hitchhiker's Guide to the Galaxy, Douglas Adams
I Am Legend, Richard Matheson
Interview with the Vampire, Anne Rice
The Left Hand of Darkness, Ursula K. Le Guin
Little, Big, John Crowley
Lord of Light, Roger Zelazny
The Man in the High Castle, Philip K. Dick
Mission of Gravity, Hal Clement
More Than Human, Theodore Sturgeon
The Rediscovery of Man, Cordwainer Smith
On the Beach, Nevil Shute
Rendezvous with Rama, Arthur C. Clarke
Ringworld, Larry Niven
Rogue Moon, Algis Budrys
The Silmarillion, J.R.R. Tolkien
Slaughterhouse-5, Kurt Vonnegut
Snow Crash, Neal Stephenson
Stand on Zanzibar, John Brunner
The Stars My Destination, Alfred Bester
Starship Troopers, Robert A. Heinlein
Stormbringer, Michael Moorcock (But I have read John Barnes' Mother Of All Storms)
The Sword of Shannara, Terry Brooks [a series I just couldn't get into, no matter how hard my then g/f tried to involve me]
Timescape, Gregory Benford
To Your Scattered Bodies Go, Philip Jose Farmer
I've read 38 out of 50, a testament to my reading habits. Several of the books up there shouldn't be there, in my not so humble opinion, while other, important volumes are missing. Isn't that the way? And only fifty! Surely, if the members of the Book Club put their collective minds in gear, they could come up with an even one hundred, don't you think? After all, where's Spider and Jeanne Robinson? Piers Anthony? Margret Atwood? John Varley? Kate Wilhelm?