I read voraciously as a kid (one of my absolute favorite hangouts was the public library), but I only remember truly loving a handful of titles, which I often read over and over again:
The Secret Garden (read it at least 10 times)
The Little Princess (again, read it over and over)
Roots (who knows how I picked this up, but I read it 3 times!)
Ramona Quimby books
Little House on the Prairie books
Roald Dahl books (though they creeped me out occasionally)
Wrinkle in Time books (though I think they were way over my head, then)
A ton of fairy tales (I had a Brothers Grimm collection that I wore out)
Encyclopedia Brown books (does anyone remember those?)
Babysitters' Club books (my best friend loved the Super Specials and gave them to me)
Sweet Valley High books (I know, I know... I went through a phase!)
The Robert Jordan fantasy books, I forget what they're called now
I find it strange that I didn't really get into Narnia until much later, and most of all did not read any of The Lord of the Rings until my 20s (before the movies came out). But again, I don't know if I would have gotten as much out of reading them at a young age, who knows. I think I would have loved Harry Potter if it had been around in my childhood... but it was just as good in my 20s.