Clockwork Princess, no doubt.
If you've followed me for a while you know that Clockwork Princess is one of my favorite books of all time.
It's the last book in the Infernal Devices trilogy by Cassandra Clare.
I loved it so much because no book ever have kept me going like that, I'm not kidding when I say that I thought that I would die because of all the feelings that book upraised within me. That book is just painfully beautiful and I would love to read it again without knowing what would happen if I could.