The Phantom Tollbooth is amazing
A Wrinkle in Time series
Anne of Green Gables series (my personal favorites - I own everything the author ever wrote)
The Westing Game (really good figuring out a puzzle type of book)
Bridge to Teribithia
Hardy Boys/Nancy Drew series

You probably know all of these, but they are all such fantastic books I just had to mention them. Actually I could just go on and on - I love to read! smile