This list was originally written several years ago, and posted to a blog I no longer update. I still think it's a good idea and didn't like the thought of it sitting, ignored, on that blog, so I'm updating it and re-publishing it here.
These are books that not only make the reader think, but make an important impact on their lives. These are works that will make the reader a different person, a more complete person. They will show the reader things about themselves that they might otherwise never come close to realizing.
Notes from Underground by Dostoevsky. This is to be read before you turn 30. It's not as popular as some of his other works, but it appeals directly to a younger reader. The narrators broken, paranoid mind is wonderful to read, until you realize you've shared his thoughts.
"I am a sick man... I am a wicked man"
Read anything by James Joyce. If nothing else this will be your excuse to never, ever, ever, read real literature again! It will be the most difficult thing you read and possibly the most rewarding. (super bonus points if you choose Finnegans Wake... and tell me about it, I've been trying for 4 years to get deeper than 40 pages into it!)
"His soul swooned slowly as he heard the snow falling faintly through the universe and faintly falling, like the descent of their last end, upon all the living and the dead."
The End of the Affair by Graham Greene... if you've ever been in love with someone after they've forgotten about you this book will be a poignant reassurance that it's happened to everyone.
"The sense of unhappiness is so much easier to convey than that of happiness. In misery we seem aware of our own existence, even though it may be in the form of a monstrous egotism: this pain of mine is individual, this nerve that winces belongs to me and no other. But happiness annihilates us: we lose our identity."
J.M. Coetzee. Read either Disgrace or Life and times of Michael K. Proof that you don't need huge words to deal with huge topics.
"and in that way, he would say, one can live"
Interpreter of Maladies by Jhumpa Lahiri. These are quite literally some of the best short stories ever written. The first story in the collection will make you want to cry but reading this collection together will take you through an amazing arc. You will be amazingly depressed at the beginning and by the end you will be amazingly optimistic.
"I know that my achievement is quite ordinary. I am not the only man to seek his fortune far from home, and certainly I am not the first. Still, there are times I am bewildered by each mile I have traveled, each meal I have eaten, each person I have known, each room in which I have slept. As ordinary as it all appears, there are times when it is beyond my imagination."
UPDATE:
Added handy links for your shopping convienence!