XD
"Let's see. A human hooks up with a cute nonhuman chick with huge eyes after being altered into something more to her scale. He learns about a gorgeous rainforest, doesn't exactly hit it off with the locals who are One With The Forest, and ends up battling an industrial force plundering the landscape alongside said forest dwellers after having an anvil dropped on him. Hmm. Avatar only lacks a manifestation of pollution voiced by Tim Curry. But that would have been awesome."
"Man comes from another world to harvest a rare mineral unique to only this extremely hostile moon. Ends up being forced to live among the natives and learn their ways from a local girl who he ends up falling in love with. Has to ride a fearsome creature as a right of passage into manhood, and then unites the local clans and leads them to battle against culture from which he originally came. Can you say Dune?"
"A war between nature and industry over precious resources hidden in the ground culminating in a violent encounter and attacks against the forest gods... Huh... " (this one linked to Princess Mononoke)
"Minus the avatar (and the coloring of the aliens) the plot is identical to Ursula K Le Guin's The Word for World is Forest, right down the General Ripper Big Bad. Except for the bit where The Word for World is Forest was culturally rich and morally complex, of course."
"A giant, surrealistic forest that contains an atmosphere that humans cannot breathe without dying? Hmmm..." (Nausicaa of the Valley of the Wind)
"Let's see... something that comes from the skies and wreaks descruction upon the world and is defeated by a race close to nature. A disaffected soldier who assumes a dead man's identity (in this case, his avatar). A female character who is mortally wounded by the main villain and dies, but in doing so merges with the planet's conciousness. Trees that glow white. Allegories to Big Oil. Imperialistic corporations. An attack from the planet itself that sends the bad guys packing. Final Fantasy VII, anyone?"
All taken from the TVtropes page for it. TVTropes: Avatar.
Also, I apologize for linking to tvtropes.