Spoilers...

1 - Lord of the Flies by William Golding: the bit where the rock gets dropped on Piggy - that one knocked the wind outta me i can tell you. But perhaps the other bit that really stands out is the passage where i think Roger is spying on one of the littluns playing with a sea creature and is enjoying exercising control over a smaller, less powerful entity. Then i think Roger starts to throw stones at him.
2 - The Bell Jar by Sylvia Plath: a cliche book to choose but i always remember that bit where she writes about the fig tree and each fig represents a different choice or path she can take but they all look so tempting and the longer she stands there pontificating the figs slowly begin to dry up and die.
3 - NY Trilogy by Paul Auster: The bit where Peter Stillman recounts in a multi-page monologue how he was locked in a room for years. Made the hairs on the back of my neck stand up. brrr.