Dog Man Unleashed (Dog Man #2)
While I was a bit disturbed about Dog Man's genesis (both a police man and a dog are so badly injured that doctors have to cobble the two together), my students don't seem to care much about this. It's funny to see a person acting like a dog and vice versa. It did occur to me that people will probably be gravely offended by the picture of Dog Man sniffing a poodle's butt in the pet store and accuse Pilkey of harassment. Nota Bene: None of these people will be eight years old.
This series has the same level of goofy adventure that Captain Underpants has, and Dog Man is as headstrong as George and Harold. Pilkey never really needs any recommendation-- his books just fly off the shelf, and Dog Man will be no exception.