Princess Mononoke
Coming out a couple of years before the award winning Spirited Away this is the film that led the way. It pays much more attention to Western audiences and has a reasonable dub, although I prefer subtitles. It deals with environmental issues, a common theme in Miyazaki's work, but also acknowledges that progress can bring benefits. Many characters' actions cannot be considered as good or evil but hover somewhere in between.
I particularly liked the Kodama, tiny white forest spirits, with strange heads (but in a good way.)