I agree with Pastoralan that books seem to lose points the farther they are from NAO and GoB - is Genji the only non-western book mentioned so far? So taking out what's already been mentioned, I'd probably include these:
1) The Mahabharata, Vyasa
2) Journey to the West, Wu Chengen
3) The Romance of the Three Kingdoms, Luo Guanzhong
4) If on a Winter's Night a Traveler (or The Path to the Spiders' Nests), Italo Calvino
5) The Unbearably Lightness of Being, Milan Kundera
6) A Dictionary of the Khazars, Milorad Pavic
7) Snow (or maybe My Name is Red), Orhan Pamuk
9) 100 Years of Solitude, Gabriel Garcia Marquez
9) The Shahnameh, Ferdowsi
10) The Alexandria Quartet, Lawrence Durrell (I know, I know, he's English)
The western books - even poor maligned Gatsby - are obviously great (except maybe Rowling and Pullman - "engrossing" might be more appropriate). But I think these definitely belong as half of a top-20 list.