My 11 year old DD has recently been flying through the Fablehaven series, which was recommended by a male friend. Ranger's Apprentice books are very popular with some fifth graders I know. Also "Things Not Seen" by Andrew Clements, which my kids didn't pick up, but which has been a huge hit with some other readers I know (the main character wakes up to find that he's invisible).

I also highly recommend Jonathan Stroud's Baritmaeous trilogy (beginning with the Amulet of Samarkand). It takes a little bit of time to get into, but it's a great read, and the chapters narrated by Bartimaeous are filled with wry humor in the form of footnotes.