A Wrinkle in Time, by Madeleine L'Engle, is one of my favorite books, and it's because I first read it when I was maybe eight. The novel follows Meg Murry, a twelve-year-old, self-conscious outcast, who is busy coming to grips with the disappearance of her father and protecting her precocious younger brother, Charles Wallace, from the bullies at school. When a mysterious visitor named Mrs. Whatsit appears in the middle of one "dark and stormy night," and makes her mother faint with the enigmatic words "There is such a thing as a tesseract," Meg finds herself thrust into an adventure across the Universe, to save her father... and maybe the world?
This book was a great source of comfort to me as a kid, because it was nice having someone to read about who wasn't necessarily the smartest, coolest, or most "special," but who was definitely still the hero of her own story. It's one of those things that I still find comforting to read today, that even supposedly ordinary people can also have great adventures (especially when I come back from a class leaving me feeling about as dumb as Meg felt about school, too).
More impressive is the fact that A Wrinkle in Time was one of the first popularized science fiction novels to make a significant culture impact AND have a young, female protagonist, something virtually unheard of at the time of its first publication in 1962. It's remained continuously in print since then, which is a pretty significant accomplishment in itself, but the fact that L'Engle is essentially responsible for raising the people who write strong female characters in YA fantasy and science fiction today, is pretty damn cool.
Here's my favorite look from the post, inspired by the droll, doll-like qualities of the people on Camazotz, ruled over by the dark and oppressive "IT."