Hi Heather, just off the top of my head...my son loves the Warrior series and Deltora Quest. He says the best book he has EVER read is The Westing Game.
I have to get back with you on my daughter's favorites. (Although she is telling me that everyone in her class LOVES the Twilight series) :)
Harry Potter, Twilight Series tho Breaking Dawn was a little more for teens not preteens. The Inheritance Series is really good. my stepdaughter enjoyed it alot
Twilight series is the most popular books going right now. Of course, you know about Harry Potter and Lemony Snicket. The Alex Ryder series is one I haven't seen mentioned that my son likes a good bit.
Umm...can it be MY fav? Twilight. Most definitely. Harry Potter, of course. Another of my favs. I love young adult and pre-teen books. A little weird, I guess. And Tiger Eyes by Judy Blume. That's a good one.