I'm a great fan of historical fiction, particularly in children's literature. In the Guardian's Book Blog, Imogen Russell Williams has posted a wonderful article outlining the value of children's historical fiction, not just in it's telling of a great story and quality of writing, but in the benefits of the stories themselves in inspiring the imagination and thought processes of young readers. She not only speaks eloquently of older fiction writers like Rosemary Sutcliffe, whose tales of Roman Britain such as Eagle of the Ninth are simply magnificent; but also of some more contemporary favourites bringing the past alive again... Kevin Crossley-Holland, Celia Rees and Sally Gardner (whose I, Coriander and The Red Necklace bring to life some brilliant aspects of history, mixed with a slight mystical content that effortlessly seems both magical and completely possible.) An article well worth reading, as are all the books mentioned.
On a personal note, I'm going to recommend The Crowfield Curse by Pat Walsh. Think of it as The Company of Liars for 9 to 12 year olds. I've put a brief over view of this on the 'What ARE You Reading' page, if you want more information.