Ann M. Martin--Yes, I was one of those girls. I read every single Baby-Sitters Club book, and when I was too little to read those books while my sister was reading them, I got all of the Baby-Sitter's Little Sister books. I have also read some of Martin's more powerful stories like Ten Kids, No Pets, and more recently, I was blown away when I read A Corner of the Universe. I remember my fourth-grade teacher reading Ma and Pa Dracula to our class, and I think I still base every vampire book I read against the myths Martin established in that book. Ann M. Martin was a staple of my childhood reading.
Pamela F. Service--Service was really my introduction to science fiction. After reading A Being of Two Minds, I think I went to the library and checked out every one of her books. A few years ago I went on a quest to find a copy of Weirdoes of the Universe Unite, a cooky story of misfits from mythology who gather to save the world. Because the book had been out of print for probably ten years or more, I finally found a used copy for sale online--it was the best 99 cents I have ever spent. Her post-apocalyptic version of Arthurian legend even influence my minor in college.
Caroline B. Cooney--The Face on the Milk Carton was probably the first "romance" novel I ever read. It's not really a romance novel by any stretch of the imagination, but it talks about the main character's decision to have sex, or rather not to have sex. And I think every girl in my seventh-grade class set their VCR to record Kellie Martin play Jennifer/Janie, because who didn't want to see Becca Thatcher play the lead role in a made-for-TV movie? (That was long before her character got killed off on ER but at the same time she was playing Christy.) I tend to turn my nose up at "serial YA fiction," but really, I read just as much of it when I was younger as kids do now.
Beverly Cleary--I always tell people that Cleary saved my life, and that is no exaggeration. I moved half-way though sixth grade and was very lonely and depressed. Then I read Dear Mr. Henshaw and my life changed. For the first time, I could put myself in the shoes of a character and realize I wasn't alone. I proceeded to read every other book Cleary wrote back in the fifties and fell in love with the California Dream when I read The Luckiest Girl and wished that I could be the Sister of the Bride.
I mark time with the books I read. I remember certain events in my life in relation to the books I was reading at the time--my dad lost his job at the same time Ramona Quimby's father lost his, our family vacation to Washington, DC, happened the same summer I read my first Mary Higgins Clark book (Stillwatch, which happens to take place in the very city we were visiting), and I remember the Easter of 1993 like it was yesterday because that was when I got the boxed set of the Anne of Green Gables series. I think I have been obsessed with books a lot longer than I realized.