Into the Wild by Jon Krakauer. Great short book about a young man's ill-fated journey of self discovery. Really sad at the end; I can't shake the image of his skeletal frame and reading about his last days.
Life of Pi by Yann Martel. Fantastic book about a young boy's journey on a boat with a tiger.
Frankenstein by Mary Shelly. You'd be surprised how many haven't read this story. It's great.
This Much I Know Is True by Wally Lamb. Gripping story about a brother's dealing with his twin's paranoid schizophrenia. Really great book.
A Thousand Splendid Suns by Khaled Hosseini. Same guy who wrote The Kite Runner. This is a phenomenal book; I cried buckets.
A Prayer for Owen Meany by John Irving. It's kind of a book without a plot,IMO. What a fantastic, fantastic, book.
On Beauty by Zadie Smith.
I have plenty others. I'm currently really heavy in a vampire/wolves/witches stage, so I'm obsessed with:
Kresley Cole-Immortals after Dark series. Warning: you will become addicted!
J.R. Ward-Black Dagger Brotherhood series. So good. Just so damn good. Rhage, Zdadist, et al. Sigh.