Un Lun Dun by China Miéville

This book was so good, it had me foisting it on people almost before I was done reading it myself. It's the story of two young girls who find themselves drawn to Un Lun Dun, a sort of mirrored version of London, where broken and un-used things often find themselves, and a world menaced by the Smog (a problem which London appears to have solved). In addition to the sheer pleasures of Miéville's inventiveness and imagination, the book manages simultaneously to send its heroine on a quest and mock the conventions of the quest genre. I might not give this to kids who haven't read Harry Potter--it's so good, they might not find Potter quite as satisfying when they get around to him!