I've read all five of the Song of Ice and Fire books and am dying for Winds of Winter to be released. They're a must read if you're as big of a nerd about the show as I am. Storm of Swords is one of the best books I've ever read.
Sticking with the fantasy genre, I've also read The Hobbit and LOTR, but it was many years ago. I do remember enjoying them, but not as much as ASoIaF. Probably because I'm older and am into darker stuff now...
1984 is possibly my favorite all-time book. Animal Farm is a classic as well. As a general rule, anything by Orwell is great...
Catcher in the Rye is another one of my favorites, though I know many people hate it. So many great one-liners from Holden.
I've read Great Gatsby and found it to be very overrated. I just thought it boring.
Another classic I've always found to be overrated is Slaughterhouse Five. People have sworn to me that Vonnegut is must-read material, so maybe I need to read more of his work.
Read Lord of the Flies in high school as well. Don't remember everything about it, but I did enjoy it.
Most of my high school classmates hated Life of Pi (years ago), but I thought it was outstanding. Sorta makes you think in the end, which I can appreciate...
Currently reading For Whom the Bell Tolls. Just started it.
I want to read Paddle Your Own Canoe by Nick Offerman next.