Nana is HUGE in Japan. It's a cultural event. And there's a reason for that. It's about two girls named Nana living in the same apartment who, on the surface, seem different as night and day but they have a LOT in common.
The manga... is great. It's currently running in Shoujo Beat and published by the same company in book form.
The anime... is also good. It's exactly like the manga, just a bit faster paced. Nice to see how the music would sound, how the characters would look and all that. It's much more in depth than the movie.
The movie... is decent. It's only an hour and a half and you can't tell the story of the Nanas in that short a time period.
You can check out the anime and movie (both unlicensed in the US on youtube.com)
Check out this site for more info: http://nana-nana.net/