Picture-book-wise, I loved (still love it, actually) Alexander and the Terrible, Horrible, No Good, Very Bad Day (Judith Viorst.)
Getting into chapter books, the Ordinary Princess (M.M. Kaye) has always been one of my favorites. I was really into the Babysitters' Club and Sweet Valley books for a few years.
Others:
From the Mixed-Up Files of Mrs. Basil E. Frankweiler (E. L. Konigsburg)
The Wish Giver (Bill Brittain)
Remember Me to Harold Square (Paula Danziger)
The Witches (Roald Dahl)
Pretty much any L.J. Smith book, especially the Vampire Diaries & the Dark Visions trilogy
All of the Narnia books
...I read a lot as a kid. Mom made it a rule that I could only order three books from the monthly Scholastic book orders, because otherwise, we would've gone broke