Harry Potter and the Prisoner of Azkaban (Book 3)
I must admit that this book must be my near favorite out of the whole series. I think it was Sirius and Lupin that made the series even greater and the Dementors were a bunch of nasties. I think it was also knowing that somehow things were going to get even more exciting than they already were. And Harry's patronus and his father's connection to it made it even more special.
