Spirited Away
Incredibly rich movie thematically speaking. Almost feels like Miyazaki's commandments for children and parents on emotional growth and the cultivating of youth into members of society.
Chihiro begins as a timid girl but ends the movie as a strong, generous, adventurous and wise young lady.
Some of the themes of note are the need for new experiences and challenges in order to grow (ie big adult baby, plus just chihiro in general), the need to contribute to society in order to be valued (Yubaba's bathhouse, sidenote: i had thought this was miyazaki trying to say to be valuable you must work although I've heard it may also be interpreted more as a critique of capitalism), the importance of identity (through the use of names and their power), and the value of having new experiences especially with people and things which you are unfamiliar.