This is from AvatarSpirit.net, it turns out that the high quality trailer is up.
Due to the overwhelmingly positive response from Avatar fans, Nickelodeon has released a high quality version of the season 3 trailer originally shown at SDCC! Even more generously, Nick has given ASN permission to offer the trailer for download to the fan community. Click on the link above or on the graphic at left to view the trailer in Quicktime.
To download the awesomeness that is the SDCC Season 3 Trailer, right click on the link or the graphic and choose "Save Link As"! The trailer is a .mov file that I was was able to play on Windows Movie Maker, DivX Player, Total Video Player, Quicktime and Realplayer. It's quite large (over 400 MB), so those on dial up may want to shy away.
EDIT: Here is a lower resolution copy that is only 33MB for those having trouble downloading the full size version!
Nick has made one request of the fan community, and we pass it on here for everyone to read. Please do not post this video on youtube or any other file sharing service. Such videos will be removed immediately. Nickelodeon has generously allowed us to host it here, and other fansites are free to post it as well so that everyone in the community can enjoy this awesome bag of goodies! If you would, though, please honor Nick's single request in this matter and refrain from posting it on the video sharing sites. That said, a lot of new details are sure to be observed with the release of this high quality copy, so let the discussion and speculation begin anew! And a great big thanks to Nickelodeon for sharing this with the fans!
Lastly, for those who want great shots for their signatures and avatars, we have created a set of 267 screenshots for the trailer. These are all available in the "SDCC Season 3 Trailer" entry in the "Specials" section of the ASN Episode Guide. Enjoy!
I MUST WARN YOU THOUGH, IT IS HEAVILY TRAFFIC, SO YOU MAY WANT TO DOWNLOAD LATER.