Abhorsen Trilogy is Garth Nix ( Sabriel, Abhorsen and Lirael).
My older boys read my books when they were that age, mainly fantasy stuff, but the others don't bother even looking at them. I sometimes read their's though. I love Artemis Fowl 
Think Rosemary Sutcliffe might be a bit too young for a 14 year old. I mentioned it to DS1's English teacher when he was about that age and the teacher kind of scoffed.
Marcus Sedgewick books are quite good. Cornelia Funke is worth a read as are Kevin Crossley Holland's Arthurian books (The Seeing Stone, The Crossing Place and another one that I can't remember it's name.)
Classics like Lord of the Flies, 1984, Animal Farm, OF mice and Men and the Pearl and old ones like Dracula, The Invisible Man and Dorian Grey are challenging reads for this age group.
Neil Gaiman might be worth a look. Markus Zusak is quite good as well.
Howl's Moving Castle was well received by all my kids
Eion Colfer's books for older kids are fab, The Wish List, the Supernaturalist, ones like that.
Jeanne DUprau - City of Ember
James Daschner's Maze Runner books
Catherine Fischer.
I'll keep thinking about it. Over the years, we have had so many author's and books that it's hard to keep track, to be honest, but I might remember some more.