ncola, I read "The Once And Future King" when I was 9 years old b/c it was required summer reading for my older sister. I remember wanting to read it b/c a) I was (and still am!) a major bibliophile, b) It was the thickest book I had ever seen in my life and c) I wanted to do everything my older sister did.
I might not have understood everything, but I managed to read the entire thing that summer.
I just got done reading "Citizen Girl", by Emma McLaughlin & Nicola Kraus, the authors of "The Nanny Diaries". I highly, highly recommend it.
Keep the lists coming, girls! I'm writing down some of these authors for when I go to the library tomorrow.