Number the Stars? Lois Lowry's novel is the gold standard for adolescent Holocaust literature. I can't think of any novel (and I have read a ton of them) that better introduces the tragedy in a gentle yet informative way. I am so happy that it continues to be read and cherished by students. I remember reading it when it was first published and my sixth graders currently list it as one of their favorite novels.
The story of Annemarie Johansen's family and their efforts to save their Jewish friends is a beautiful example of loyalty, courage, and friendship. If you haven't read Number the Stars since middle school, it is worth reading again. It definitely stands the test of time.
The Egypt Game when I was growing up. I was fascinated by the chart of hieroglyphics on the wall of my social studies classroom, and spent way too much time trying to write my name using birds and other symbols. Protagonists April and Melanie do this, and more: they recreate Egypt in a vacant lot in their neighborhood, using research and their imaginations to make it as realistic as possible.
Published in 1967, the novel introduces readers to childhood before video games and television. While parts of the novel seemed to drag, at the same time there is so much story packed into this novel. It's interesting to note that a neighborhood child murderer was a casual plot point in the 60s, something that would be very controversial today. Still, I hope that today's readers are inspired to engage in more creative play after reading The Egypt Game.