Another nice series is the Penderwick Sisters. They are newer books, but have an old-fashioned feel. I see a lot of great ones listed above. We've often gone with Newbury winners, and anything by E.L. Konigsburg, is great, too.
I absolutely "ditto" all comments about ignoring Lexiles. First of all, I can't even guess what our adult lexiles would be (1500+? 2000+? does it go up from there?), but most of the best-selling books are only around 700-950. Extremely Loud and Incredibly Close, for example, which I recently read, has a lexile of just over 900. Does that mean it can't be of interest to me, just because I'm capable of reading something supposedly more difficult? Of course not. Most NY Times best sellers (things like Jodi Picoult books, for example) are often only in the 700's. I encourage anyone who is at a school that absolutely requires the children to read in their lexile range, to point this out to the teacher. You can even ask them what they have been reading in their personal time, and show them the lexiles :-)
But I do agree that highly capable readers should intersperse some more challenging vocabulary/sentence structure into their reading, so the classics can be great for this! They contain age-appropriate content, but are more challenging than current books.
I do think my own daughter had a temporary phase of being turned off from reading, and it may be that she was reading overly-challenging, or boring-to-her books. Once she settled into some books that were more enticing to her, she got right back into it, with gusto!
Good luck.
