Betsy Bird of Fuse #8 pointed me at this fascinating blog post from Empire Magazine's website: Harry Potter movie posters through the years. It's a neat little encapsulation of the changes from the first book/movie to the last, in character and tone.
I particularly like how Ron went from being the silly sidekick to (finally!) more dark and interesting in the posters for the last two movies. That's always annoyed me about the movies, that Ron, who is a goofball but brave and smart in his own unique way in the books, got relegated to comic relief while Harry and Hermione got to do all the good stuff. Naturally, the Ron bits were my favorite part of the most recent movie, because he got a lot of good stuff. Huzzah!