Here is a reading list I put together for 11/12 years olds - it grades the books by difficulty and gives a brief description of the book. If you clink on the link for each book it takes you to a more detailed description.
Sophie Mckenzie is a popular author to follow on from Jacqueline Wilson. She's not a classic author but is a good read. More classic for an 11 year old is Bridge to Terrabithia but other good books are Soldier Dog and Mortal Engines.
Please can anyone suggest some books/authors for my 11 year old girl? She likes girlie stuff like Dork Diaries, Jacqueline Wilson, Enid Blyton etc but I wanted her to try something new and possibly a bit more grown up.