These five books all tie. Each and every one of them are awesome and must reads.

To Kill a Mockingbird, by Harper Lee
Killing Mr. Griffin, by Lois Duncan
The Giver, by Lois Lowry
Roll of Thunder, Hear My Cry, by Mildred D. Taylor
A Picture of Freedom, by Patricia C. McKissack

Each of these books are extremely well written, have complex yet understandable plots full of twists and turns, and can be deeply analyzed. All of them have powerful endings. Very unforgetable books.