Pfffft! Like anybody will read in 300 years.
Apples and oranges. How many books were there in 1709? How many people even could read?
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I agree that Stephen King is one of the more likely authors to be read in 300 years. He’s just a great storyteller. Unlike Shakespeare, however, there won’t be “The Complete Works of Stephen King.” A lot of what he wrote is utter dreck. But much of his stuff will survive.
The interesting question is which of his works will endure?
While that is a valid point (the relative scarcity of literature in the 17th-century contrasted with our current over-abundance), my point is also that that is what was popular then. People couldn’t get enough of stuff that bores the pants off current English majors. I would be very surprised if 300-years-in-the-future readers would find King even remotely interesting. “Mom, do I have to read The Stand? This is sooooo boring. Let me download the Spark Notes into my brain instead.”
Plus, everything will have to translated in to binary. For our robot overlords, of course.
A question worthy of its own thread. Lots of King readers here.
His early stuff, for sure – Carrie, The Shining, Salem’s Lot, The Stand. Definitely not Tommyknockers. 
Who else? How about some of the newer mystery/crime writers? People still read the Sherlock Holmes stories, and Agatha Christie’s books. I can’t see John Grisham holding up, but maybe Elmore Leonard and Richard Price and John Connolly will.
I nominate manga. Some of Tezuka Osamu’s stuff will survive (I’m thinking the Phoenix cycle & Apollo’s Song rather than [del]Astro Boy[/del] Tetsuwan Atom, but who knows?), maybe a little Takahashi Rumiko, & very possibly Miyazaki Hayao’s Nausicaä of the Valley of Wind.
Some of Ikegami Ryōichi’s stuff should survive just for the artistic quality.
Actually, I believe that linguistically, our language (English), has entered a common era and simplification. I think the standard English of 2360 will be intelligible to our writ and perhaps derivative.
The Harry Potter books, very likely (though they don’t all count as 20th century). Ditto Narnia and possibly Charlie and the Chocolate Factory. Alice in Wonderland and Peter Pan are almost certain to still be read for fun then. Children’s books seem to endure longer.
Agreed about LotR and probably Christie and King.
Other than that, I really have no idea when it comes to adult books. I’d be surprised if many comedies survived. Perhaps one or two (such as Hitchiker’s, if the world has any sense at all), but comedy tends to be too culturally specific and time-dependant.
One of the reasons we don’t read much from around 1709 is that the novel was then a relatively new development, and many novels of the time still didn’t fit our current definition of a novel. (The Wiki article about the novel in the 18th century is more scholarly than most). We tend to think of ‘books’ as having been around ever since literacy has been, but they’re a modern phenomenom. It’s hard to talk about which novels were popular then because there really wasn’t much competition.
Gone With the Wind.
The Big Sleep.
The Maltese Falcon.
Robert E. Howard’s Conan stories.
The Collected Forum Posts of bup.
That line has always worried me. What made the writers think those authors would even be archived?
But then, Kirk is an esoteric guy.
What people don’t often notice in the formation of language is that Spanish is a descendent of the Latin dialect of that province, A whole new language descendent, supplanting gaelic. Some people devaluate the influence of a Lingua Franca, that which morphs. Anybody remember Falco? I’d love to see the Englisch of the provinces become new morpholinguistic languages.
I don’t understand this post at all. Are there really many people who are unaware that Spanish is related to Latin? What does Gaelic have to do with it? Falco? Lingua Franca meaning that which morphs? 
Sorry - maybe I’m just being dense.
How about To Kill a Mockingbird? Or will the (hopefully) lack of racial issues in 300 years make it irrelevant?
I think that often experiments and their devisers miss seminal moments because of political distraction and bad timing. Now, is the momernt for reticent linguists. Never before, never again.
I hope we keep having sex until by then we are all the same color, but as for TKAMB, oh yes. And one must add In Cold Blood.
I think in 100 years, people will look back and wonder why the Harry Potter books were so popular, and in 300 years they will almost certainly have left the public consciousness.
I think a modern classic, but that only goes 50 years or so, will be The Time Traveler’s Wife.
Some nut in 2300 will still read Umberto Eco’s, Foucalult’s Pendulum and start a secret society, for or vehemently against the Illuminati, or the NWO, or the Black Irish—is yet to be seen. Just like the other Roman literature from thousands of years ago.
Maybe Lolita will be read also. In 300 years, people may be wondering what all the fuss was about over this book and why it was considered so shocking.
I don’t think people will read books in 300 years. Hell, they don’t now.
I can’t see a world without libraries. Format might change, but the library is eternal That is why I am offended, and frankly feel as a pawn between my Governor Strickland (Ohio Governor, Democrat) and a shrewd and political ploy threatening our common font of knowledge.