I decided to split middle school and high school up. Why? Because they're my lists, I suppose.
To Kill a Mockingbird by Harper Lee--This is one of my own favorite books, and I was sort of surprised when Cubby read it in class in fifth grade. I mean, the main character is a young girl, but I feel like there's just too much going on in the story that would go over the head of an elementary-aged kid. I think middle school is a good time to read this book for the first time. Subsequent re-readings will reveal more and more, but a seventh grader can get plenty out of it on the first reading.
A Tree Grows in Brooklyn by Betty Smith--Another of my personal favorites. Such a great glimpse into life in early twentieth century Brooklyn tenements. Great characters, too.
The Adventures of Tom Sawyer and The Adventures of Huckleberry Finn by Mark Twain--My boys have a slight preference for Huck Finn, but agreed that readers new to Mark Twain should read Tom Sawyer first.
The Winter War by William Durban--A historical novel about a teenage boy who helps fight the Soviets when they invade his home of Finland.
Anne of Green Gables by L.M. Montgomery--I do not love the Anne books as much as I did when I was younger, but I still think everyone should read at least the first one.
Hatchet by Gary Paulsen--I didn't put this one on the elementary list because I think some of it is better for middle school. Gary Paulsen's style doesn't always produce a straightforward narrative, and the stuff about the main character's parents' divorce is probably more for older kids. Such a great book, though. One of my favorites when I was a kid, and a favorite of my sons', too.
Bridge To Terabithia by Katherine Paterson--The best book for kids that is almost guaranteed to make them cry. Maybe not the best for very sensitive children, but a great book nonetheless.
Julie of the Wolves by Jean Craighead George--I loved this book about an Eskimo girl who must learn to survive on her own. I don't think my sons have read it yet. Must get it for them.
Any Calvin and Hobbes by Bill Watterson--I can't believe I forgot to put this on the list! Any and all of the Calvin and Hobbes comic collections are beloved of my children. And by me, too, although I now find myself identifying more with Calvin's mom than with Calvin. They are surprisingly sophisticated in both language and content, and just very, very funny.
What would you add to this list of middle school fiction?