My Top Picks for Girls:
The Nancy Drew series
The Little House on the Prairie series
Treasures of the Snow
My Top Picks for Boys or Girls:
Swiss Family Robinson
The Sugar Creek Gang series
The Hardy Boys series
Peanuts Comic Books
A lot of books you will find on classical reading lists are not of interest to preteens living in 2013. That said, I feel that older books teach better morals and have more educational value than the dumbed down children's books of today. I like my children to read the above books from the late 19th and early 20th century that I enjoyed as a young girl. I don't remember how old I was when I started reading these books, but I'm pretty sure I was still reading some of them by age eleven. I read most of the books on the list voluntarily for pleasure, not knowing that they were educational.
I think my mom read some of these books in her own childhood which is why she bought them for me. I didn't have a lot of books so some of them, including Black Beauty, were read more than once. The Sugar Creek Gang books and Treasures of the Snow were books I had to read for school but enjoyed immensely.
I read a few other books, but the ones on my list are the more memorable ones that I recommend. Since these old books were still interesting to me in the late 70s and early 80s, they have obviously withstood the test of time. I'm sure there are other fun classics that I hope to discover and pass on to my kids, but the books on this list are my personal favorites from my own childhood.