I like "ender's game", it should be in the top ten!

another references are "blindness essay" by saramago, and the short but impressive tale "schachnovelle" by stefan zweig

The constant inclusion of 1984 is a really sad reflection on the literary sophistication of this group...

Also, @dexter_morgan - While I disagree with Tolstoy's assessment of Shakespeare, it isn't based on wishy-washy vague terms like "sincere". There is such a thing (or at least, such a thing as a very serious attempt to establish) some sense of clear aesthetics for determining artistic merit.

I think you know this, since you're unlikely (except to make a point) to really commit to a position such as "The only reason Picasso is said to be better than my six year old's finger-painting is arbitrary, vague standards of quality coupled with longevity". If you take that sort of statement to be untrue in some way, you'll have to concede that there is some structure of aesthetic judgement, and that disagreements about what constitutes that struct does not imply its non-existence.

1984 is a great book, sorry if you don't think it's sophisticated enough. Not in the top 5 but definitely top 10, I would say perhaps that it shows a lack of diversity but not of sophistication. If we include graphic novels, V for Vendetta goes on the list

"1984 is a great book". Maybe it's just me, but I really don't rate it. Sure it's got an interesting message, but it isn't a very good book. The story is very obvious, and the only real reason to read it is for the letter.
How about Catch-22?

The prose are refreshingly concise in a way that Orwell always is, but the themes aren't particularly nuanced, nor is the plot very compelling or innovative. Brave New World is far and away the better dystopia, and even that isn't a great book.