Very few... Maybe JD Salinger, Vikram Seth, and some others I can't seem to be able to name.
A classic is made by its timelessness. Some stories never grow old. They just change the world in a way. And each generation deems them worthy enough to be passed on to the next. And some others are classics in that their importance is yet to be discovered. After all, Herman Melville was never celebrated for as long as he lived. HG Wells gained importance when many of his stories turned out to be predictions of a sort.
I find it hard to believe that any fantasy book of this day and age will last another decade or so. Maybe Harry Potter will exist as a children's classic. I definitely can't see A Song Of Fire And Ice or The Wheel Of Time lasting that long. Sad though that may be.
Then there're other books. Crime and murder mysteries will definitely not last that long. Grisham, King, Ludlum, Crichton... I don't see any of them being studied eighty or so years from now....