Official site:http://www.nick.com/shows/avatar/index.jhtml
Information about the anime:http://www.wikipedia.org

One hundred years before the start of the series, a 12 year old Airbender Aang learns that he is the new Avatar. Fearful of the heavy responsibilities of stopping an impending world war and with the impending separation from his mentor Monk Gyatso, Aang flees from home on his flying bison Appa. During a fierce storm, they crash into the ocean, and Aang's Avatar state freezes them in a state of suspended animation inside an iceberg.
Aang and Appa are awoken a hundred years later by two siblings of Southern Water Tribe origin, Katara and Sokka. Aang learns that the Fire Nation started a war a hundred years ago, just after his disappearance. The Fire Nation's opening move in its campaign for global conquest was to launch a genocidal attack on the Air Nomads which drove Aang's entire race to extinction, thus making him "the last Airbender" left alive. He realizes that he must fulfill his destiny of becoming the Avatar and return balance to the world by defeating the Fire Nation. Aang sets out to master the three unlearned elements: Water, Earth, and Fire. With Katara and Sokka, Aang decides to head first to the North Pole to find a Waterbending master.After leaving the North Pole and mastering Waterbending, Aang travels to the Earth Kingdom to master Earthbending. There, the group meets Toph, a blind Earthbending prodigy who becomes Aang's second teacher. The heroes discover information about an upcoming solar eclipse which would leave the Fire Nation powerless and open to invasion. They struggle to reach the Earth King with this vital information, but are detoured by Appa's kidnapping. The psychologically self-tormented Zuko, his sister Azula, and her two friends Mai and Ty Lee chase the group as the struggle to reach Ba Sing Se. Azula engineers a coup from within that topples the Earth King and destroys any hope of a large-scale invasion of the Fire Nation.
On the day of the solar eclipse, Aang's group and a smaller band of warriors launch a smaller invasion, which fails. Zuko confronts his father and leaves the Fire Nation. He later manages to gain the trust of the protagonists and becomes Aang's Firebending teacher. Sokka and Zuko then travel to a Fire Nation prison to rescue Sokka's father and Suki, a warrior who befriended the group when they traveled to Kyoshi Island.

Season One

episode 01: http://www.megaupload.com/?d=CLRG9ICO
episode 02: http://www.megaupload.com/?d=RF8Y0DHD
episode 03: http://www.megaupload.com/?d=8AO4WEWU
episode 04: http://www.megaupload.com/?d=GCWAITN5
episode 05: http://www.megaupload.com/?d=SJFW4MIW
episode 06: http://www.megaupload.com/?d=7GAV3JMP
episode 07: http://www.megaupload.com/?d=95TVBZHD
episode 08: http://www.megaupload.com/?d=ZIAXWM8N
episode 09: http://www.megaupload.com/?d=5E7KDVAO
episode 10: http://www.megaupload.com/?d=49N5DZVV
episode 11: http://www.megaupload.com/?d=KMXHTKPD
episode 12: http://www.megaupload.com/?d=HC72EGBS
episode 13: http://www.megaupload.com/?d=4S6RCZW3
episode 14: http://www.megaupload.com/?d=HQNXL6QH
episode 15: http://www.megaupload.com/?d=FWB782RE
episode 16: http://www.megaupload.com/?d=F62OJ0RL
episode 17: http://www.megaupload.com/?d=FTWI6B8L
episode 18: http://www.megaupload.com/?d=EH3S4SSD
episode 19: http://www.megaupload.com/?d=QGU0PW5R
episode 20: http://www.megaupload.com/?d=9459YR0K

Season Two

episode 01: http://www.megaupload.com/?d=17A5O98E
episode 02: http://www.megaupload.com/?d=M6KDACTB
episode 03: http://www.megaupload.com/?d=5SSZY2MQ
episode 04: http://www.megaupload.com/?d=77CJK317
episode 05: http://www.megaupload.com/?d=EHPMGO5T
episode 06: http://www.megaupload.com/?d=O7JVR82Y
episode 07: http://www.megaupload.com/?d=BS1IDTHJ
episode 08: http://www.megaupload.com/?d=AOTIRHJF
episode 09: http://www.megaupload.com/?d=H718X1VF
episode 10: http://www.megaupload.com/?d=EZ81LCGJ
episode 11: http://www.megaupload.com/?d=KMA2DYOC
episode 12: http://www.megaupload.com/?d=8ELXYVSF
episode 13: http://www.megaupload.com/?d=F13RFPI0
episode 14: http://www.megaupload.com/?d=0NVMWTHR
episode 15: http://www.megaupload.com/?d=BMN9IKAM
episode 16: http://www.megaupload.com/?d=PYK9UY5E
episode 17: http://www.megaupload.com/?d=E01UBJ7D
episode 18: http://www.megaupload.com/?d=QMDIYZSS
episode 19&20: http://www.megaupload.com/?d=1IRBDUFG

Season Three

episode 01: http://www.megaupload.com/?d=9ZSQIO09
episode 02: http://www.megaupload.com/?d=VRJSE9KC
episode 03: http://www.megaupload.com/?d=CY1R4P40
episode 04: http://www.megaupload.com/?d=GX8FINTK
episode 05: http://www.megaupload.com/?d=W8R57GKI
episode 06: http://www.megaupload.com/?d=57BFW5BO
episode 07: http://www.megaupload.com/?d=X95KCBDR
episode 08: http://www.megaupload.com/?d=SS0J5X0D
episode 09: http://www.megaupload.com/?d=GSPL8JL6
episode 10: http://www.megaupload.com/?d=I8JNTNGA
episode 11: http://www.megaupload.com/?d=E95YHTW3
episode 12: http://www.megaupload.com/?d=CZQWD7BR
episode 13: http://www.megaupload.com/?d=K19M5LCP
episode 14: http://www.megaupload.com/?d=QFX99BT9
episode 15: http://www.megaupload.com/?d=5Q8C4WY1