When I was in middle school and on through high school I was a big reader. I attribute this to having next to no social life and not having cable a good chunk of my lifespan.
But I wouldn't take back the books I read for all of the episodes of Highlander, Forever Knight, Stargate and every other DVD boxset I can think of.
So I want to give you a list of some of the books I read before they were ever class assignments and why I liked them. If others would like to chime in with their book lists that would be great.
Flowers for Algernon
I read this one in the eighth grade. They also published a heavily watered down version of this story one of those school reading books, you know the ones.
I liked the way it depicts Charlie's progress from a mentally challenged adult, to a fully functioning and independant man and back again. It's very much a cautionary tale about toying with nature and the consequences of trying to use cold science to "improve" people we percieve to be imperfect.
Lord of the Flies
This book sums up everything I hate about group mentality. I read it in my senior year of high school and lo and behold it turned out to be a required summer reading book when I transferred from my low level English class to college level in the following semester.
Those are the only books I can think of that I read before they were explicitly assigned to me in school. Again, feel free to chime in with yours.