Wow, a Harry Potter thread. I have a feeling I will be here quite often.
First of all, the books in order, and then the movies in order, because the movies are all great in their own rights...
7. Harry Potter & the Sorcerer's Stone
6. Harry Potter & the Chamber of Secrets
5. Harry Potter & the Order of the Phoenix
4. Harry Potter & the Goblet of Fire
3. Harry Potter & the Prisoner of Azkaban
2. Harry Potter & the Deathly Hallows
1. Harry Potter & the Half-Blood Prince
I chose Half-Blood Prince because I tend to be a bigger fan of character development, and the development of Voldemort here is outstanding, not to mention all the rest of the MC's. Now, the movies are a different story...
8. Harry Potter & the Half-Blood Prince
7. Harry Potter & the Order of the Phoenix
6. Harry Potter & the Sorcerer's Stone
5. Harry Potter & the Deathly Hallows Pt. 1
4. Harry Potter & the Goblet of Fire
3. Harry Potter & the Chamber of Secrets
2. Harry Potter & the Deathly Hallows Pt. 2
1. Harry Potter & the Prisoner of Azkaban
The movie for Half-Blood Prince just omitted way too much. I suppose if you haven't read the books (and I have the same opinion for The Hunger Games movie as well), it stands as a good piece of film-making, but, again, way too much was missing here, particularly from the end of the book. Meanwhile, Alfonso Cuaron did a magnificent job in Prisoner of Azkaban, all the way down to the filmography. The whole end sequence with the colors dulled down, symbolizing the darkness of the Dementors, and, I could go on and on. It was fantastic... I shall read through what you all have written, and throw some comments in for funsies!