I agree with Lenny that there shouldn't be a sequel, but for different reasons. First off, if you haven't seen the movie, do so - enough said. I saw it in 3d and will try to make it back to the theater to see it again, this time not in 3d.

The reason no sequel should be made is because it would cheapen the epicness of the movie - the story also leaves no real need for one. Imagine if there were a sequel to Braveheart or the Titanic - neither of which make a lot of sense to do. I suppose the only difference between those two movies and Avatar is that Avatar has the freedom to create a plot device that exceeds how heroic or legendary the first movie is since it is fiction.