The Franchise: As yet just the one film, but since it happens to be highest grossing film ever made, sequels are inevitable.
The Fandom: At the time of its release, there was a brief outbreak of fervour for the immersive realism of Pandora, with Avatards expressing their preference for a fictional world populated by giant Smurfs for real life. Not much different from any other fandom, then.
Most Amazing Example Of Devotion: Any Cosplayers who are prepared to paint themselves blue. We salute you.