Someone earlier said they don't like to read books over and over, but I'm just the opposite. If I find a book I love, I will read it again and again. My mother always thought that was so weird.
Here's a list of books I've read so many times that I've actually had to buy new copies of them! (It was the only criteria I could come up with to help me make a list that wasn't so long it would bore you to tears!)
Gone with the Wind, Margaret Mitchell (admittedly, the first copy was lost when I dropped it in the bathtub. Tough lesson at age 13---don't try to shave your legs and read at the same time!)
the entire Little House on the Prairie series, Laura Ingalls Wilder (yes, I actually wore them all out and had to replace them. The first set was a gift from my aunt when I was 8 years old.)
the entire Anne of Green Gables series, Lucy Maud Montgomery
The Hobbit, JRR Tolkien
The Great Gatsby, F Scott Fitzgerald (I wrote many a paper on this novel in university! You can't beat it for symbolism and a sumptuous, lyrical prose style. Fitzgerald's style is like a frothy wedding cake! And to think the man was just trying to impress that schizo wife of his.
)
The Color Purple, Alice Walker
The Prophet, Kahlil Gibran
These are the books that stand out in memory from my childhood and teen years as ones I read to death.
I'd also like to mention that I love and value self-help books. After my divorce, I discovered the writing of Melody Beattie and have read her books over and over, particularly Codependent No More and Beyond Codependency.