The following contains plot spoilers for Avatar and for various movies to which it will be compared. If I mention a movie here, chances are the plot will be discussed. None are new movies. Proceed at your risk.
Avatar has been said to be based on so many movies that one wonders whether it is actually based on any one particular story, and instead belongs to a family of related stories. Avatar is an imaginative recombination of existing themes and story elements, and a visually interesting realization of its story, but I do think it owes more to some movies than others.
So much so, in fact, that I think that certain movies had a noticeable impact on the minds of the story's developer(s).
Click on the picture to enlarge.
I started thinking about this when I first heard Avatar characterized as "Dances With Wolves on another planet." The more I thought of this idea, the more apparent it was to me that it had much more close parallels with another film. As I finally started to assemble my thoughts on the matter, I came across the meme above. If you look at the picture, you can see some apparent similarities between Avatar and some other films. Some are more superficial than others.