Many of the novels by Diana Wynne Jones might be right up your alley. I was reading them just before I discovered Harry Potter, and I thought they were perfect for the same audience; wonderfully clever, lots of unexpected twists, lots of magic wizards, witches, etc. Plus, Diana Wynne Jones' characters are wonderfully quirky but very believable. Witch Week, Tale of Time City, Howl's Moving Castle, Charmed Life, and The Magicians of Verona are all great. My favorite of hers is Fire and Hemlock, although that one is not quite so Harry Potterish.
I also suggest The Alchemyst by Michael Scott and Alcatraz versus the Evil Librarians by Brandon Sanderson.
I also suggest The Alchemyst by Michael Scott and Alcatraz versus the Evil Librarians by Brandon Sanderson.