I don't really consider myself well read, it's hard to find both the motivation and books that really interest me. Out of what I have read though, these are my favourites:
Coraline by Neil Gaiman:
I read it when I was about 13 or 14, I can't remember. No other book has managed to draw me in as much as this before or since. I can't recall much about it, except that I found the protagonist likeable (rare for me) and that it remained on my thoughts often for months afterwards. Pretty much the definitive book of the closure of my childhood.
Brave New World by Aldous Huxley:
For me, it represents everything
Nineteen Eighty-Four (which I really didn't like) should have been. The questioning stance on modern society and morals, the future we could be heading towards, and the various attitudes of people. I think that simply the time period in which it was written helped me appreciate it a whole lot more, just because it seemed to be still so relevant almost 80 years later. It was like one small summary of what I think is wrong with everything. I didn't love this book but I did feel that it reached out to me in a way most others don't.
A Clockwork Orange by Anthony Burgess:
Really just for almost the exact same reasons as Brave New World. I see no reason to re-summarise it. Although I thought the setting and imagery was better in this book.
Sputnik Sweetheart by Haruki Murakami:
This is my most recent read, and the first in many years that I've read from start to finish in just a few days. The characters were well developed, and there was a really nice mix of reality and the supernatural and the difficulty of being able to tell the difference between the two. The book was left open to many different interpretations, which I really like. Although the beginning of the book seemed too similar to a generic (unrequited) romance novel, it soon turned into something interesting. I really enjoyed the writing style as well.
And I also feel compelled to mention H.P. Lovecraft just for his ability to write horror that I love. Horror is by far my favourite genre, but simultaneously my most hated; if it's done right then I will remember it forever, otherwise I can't stand it. I've only read a number of short story collections since I recently discovered him, but they were all very engaging and suited my taste perfectly.
NightOfRemorse said:
And Then There Were None by Agatha Christie.
A nice choice. Agatha Christie is one of those authors I wish I really would read more of. This is one novel I'm sure I will remember for a long time.