Ramona series, Mouse and the Motorcycle, Henry series, etc (Beverly Cleary)
Sideways Stories from Wayside School series (Louis Sachar)
Jenny and the Cat Club series (oldie but goodie)
World According to Humphrey
Secrets of Droon
Charlie and the Chocolate Factory (Roald Dahl)
James and the Giant Peach (same)
Matilda (same) - dark, but can really speak to gifted kids