There has been a lot of angst about Avatar The Last Airbender, and the possibility of the series ending with Book 3.  I found this at IGN.com:

Interview: Avatar’s Bryan Konietzko and Michael Dante DiMartino (September 2007)

IGN: What can we expect for Avatar’s third season? Will this season be the final installment to the Avatar world?

MIKE: This particular, three season arc will end in an exciting way that wraps up the story of Aang and Zuko. However, Bryan and I have other ideas to expand the Avatar universe, so hopefully the world will live on for a long time.

Source (page 2 scroll down)

Here is another interview done with Michael Dante DiMarino last October:

NRAMA: How does it feel to see this arc reaching its end? Do you feel like you’ve managed to accomplish all you set out to do? If so or not, why?

MD:It’s been five and a half years since we developed Avatar, so I feel a mix of sadness, accomplishment, and relief as we reach the end of this story arc. Bryan and I set out to create a show with tons of heart, humor, action and drama; a show that would appeal to kids and adults and boys and girls; and a show that raised the bar for American animation. There’s always things you would have done differently, but overall, I’m I feel like we’ve accomplished what we set out to do.

NRAMA: What can you possibly say/tell us about Avatar after this three-season arc? Will it have anything to do about the fate of the Airbenders?

MD: I’m not going to say anything. We’re still in the very early stages of development and ideas are very fluid at this point, but we’re still excited about the Avatar world and have other stories we want to tell within it.

Newsarama Note: The original article stated that there were three more seasons of of Avatar coming. According to Nickelodeon, that is not the case as of this time. We regret the error.

Source

This seems to suggest that there will be no Book 4.  However, it does appear that other stories will be told in the same universe, including the live action trilogy (this also assumes no book 4), and some animated movies.  

Check out this post, which suggests there will indeed be a Season 4, but again different story line:

Talks are reportedly underway to extend the show beyond just three seasons, which was the original plan by the creators. However, if there is a fourth season, it will likely follow a different storyline other than the Fire Lord and Fire Nation trying to take over the world, as both Nick executives and the co-creators have said season three will be when Aang faces the Fire Lord.”

Source

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Here is what we know about  “The Last Airbender” movie (Also known as “Avatar: The Last Airbender” ) :

The release date is currently set by Paramount Pictures for 07-02-10.

The Last Airbender Trilogy will be written, directed, and produced by M. Night Shyamalan. 

The first movie will be based on Book 1. 

There was a dispute over the word “Avatar”.  James Cameron has been working on a movie titled “Avatar” for some time, and so this series will not use that name in the title. 

Filming will begin in Philadelphia in May 2009. They will also be shooting in Greenland.
   

Source

The above link has a full synopsis of the Airbender story. 

Here is another Airbender Rumor:

Will There Be A Book 4? 

No. The creators confirmed that at San Diego Comic Con in July, 2007. Other stories will be told in the Avatar world and there are the upcoming live-action movies, but the animated series ends with Book 3: Fire. Nickelodeon has announced that there will be “(t)hree original 60-minute animated Avatar movies,” in addition to the live-action, feature-length film trilogy by M. Night Shyamalan.

Source – I know there are a lot of people worried about the above paragraph.  I will do some more research.  Hopefully this information is in error. 

Here are links to the bios of the co-creators of Avatar:

 Michael Dante DiMartino and  Bryan Konietzko 

Before watching the movie, you may want to catch up on old episodes.  You can watch a bunch (all of them, I think) of full episodes at Nickelodeon.com.

Watch Full Avatar The Last Airbender Episodes Here for FREE!

Or, just go buy them on Amazon.  That way you can watch it on your big screen TV:

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