Jane Eyre by Charlotte Bronte
A Tree Grows in Brooklyn, by Betty Smith. I first read this book sometime in high school, and for a while, I would reread it every year over the holidays. Francie Nolan has such an amazing spirit of curiosity, wonder, imagination, and determination, and the author beautifully illuminates some of the issues of the era through this child's eyes.
I've probably reread the Harry Potter series over a hundred times. They were the books that got me into reading at the age of 7 when we moved to a new city. Over 15 years later and I still read them with the same level of excitement.