Only 13, I remember having to check Gone With the Wind out from the library over a couple 6-week periods in order to finish it. It was the longest book I had read at the time.
V.C. Andrews (and her mystery formula) captured my attention when I was around 10. I got most of her books from a neighbor's "yard sale" bin. I continued to read these books until a few years ago.
The Sweet Valley Twins seemed like the coolest girls. I identified with Elizabeth, the "nerdy" sister who worked on the school newspaper. We even had a version of their "club" the Unicorns.