Avatar's page on Nick.com. It's under "episode guide."
All of the 'Avatar the Last Air Bender' seasons and episodes can be found on Amazon Prime.
go to youtube.com just type in avatar the last airbender episodes and from there it should give you links to some different sites.
If you want to watch it online then http://www.surfthechannel.com/ is a good place.
Youtube
You can watch them at Kumby.com
crunchyroll.com , goodanime.net , <----if you cant find it on these websites just use youtube, also chrunchyroll.com gets past school computer systems :D
on netflix
youtube
go to movies-links.tv
pinoyanime.tv in the cartoons section.
well, actually it already aired. you can watch it online in you tube. You can also watch it on anime sites like dubhappy.com and animfreak.tv
we can watch ishaan Disney episodes online at videos.apnicommunty.com