Harry Potter and The Order of The Phoenix: J.K. Rowling
On second (or maybe third) read this is a real grower. Rowling actually threads some good themes through the longest yet of the Potter stories. It doesn't beat Azkaban for me in terms of grippingness (Ithink you expect a big ole fight just now), but it is good. ANd lets face it I'm just looking forward to the Half Blood Prince now.