you have tons of great suggestions!
My 6th grade step-daughter loves reading! most of the time she's reading the Warriors series - there are tons of books in it and i think that's a big draw (she loves books when they're in a series so there's always more to read!) www.warriorcats.com
She also loves the Harry Potter series, Narnia series, Madeline L'Engle books (the Wrinkle in Time series).
She hasn't read the Lord of the Rings series yet, but we do have them in our personal library and i think they're on her list.
I'm glad noone suggested the Twilight Saga - i personally don't think its appropriate for this age group, but my step-daughter has read the first 2 books so far -- her mom allows her to read things i would have her wait a while to read (but i know, not my place to criticize what her mom allows at her home!).
And i love the suggestions of a lot of the "classic" books - i loved Frances Hodges Burnett books at that age. Her school may have a great list of suggestions too!