This is a list for all the characters that died in Avatar. Please note that there were many more deaths, but this list provides specific names.
Humans
Dr. Grace Augustine
Grace
After being incarcerated by the RDA, Trudy Chacon and Dr. Max Patel free the avatar team and then head to Trudy's Samson to escape. However, Colonel Quaritch is alerted, and, without grabbing an exopack he races out to the hangar and fires a submachine gun before using his Wasp sidearm. Although the team manages to escape, Grace suffers a critical bullet wound. Jake Sully attempts to help her live long enough to reach the Omaticaya clan at the Tree of Souls to seek Mo'at's help. After Jake enters his avatar form and manages to bond with and ride a great leonopteryx to the Tree of Souls, to the amazement of the Na'vi, he seeks their help to rescue Grace. In a trance-like state, the Na'vi and Mo'at pray, hoping that Eywa will transfer Grace's soul to her avatar body. Unfortunately, she succumbs to her wound, but before she passes away, Grace tells Jake that she sees Eywa.
Trudy Chacon
Trudy battles Quaritch's Dragon Gunship
Having defected, Trudy assisted Jake and the Na'vi during their final stand against the RDA armada, which had mobilized once more to attack the Na'vi's temporary camp on their most sacred ground. Piloting her Samson, she engaged Colonel Quaritch's Dragon Assault Ship in order to distract him from his pursuit of Jake Sully astride his great leonopteryx, but she was ultimately outgunned and killed.
Colonel Miles Quaritch
Quaritch almosts kills Jake
After Quaritch jumped out of the exploding Dragon Assault Ship in an AMP suit, he stumbled across the module containing the link unit being used by Jake, but was attacked by Neytiri riding a thanator before he could destroy it. The thanator destroyed Quaritch's GAU-90 but was killed when Quaritch stabbed it several times with his AMP suit knife, leaving Neytiri stuck beneath her slain mount. Jake's timely arrival caused Quaritch to focus on him, saving Neytiri in turn. Using the bayonet of the wrecked AMP suit's rifle, Jake was able to deflect Quaritch's attacks in a fierce bout of melee combat long enough to destroy his AMP suit knife and land a piercing blow to the glass canopy.
The damage to the AMP suit allowed the toxic Pandoran air into the suit, forcing Quaritch to don an exopack. Realizing Jake's same weakness, Quaritch made a break for the module and managed to smash it open before resuming combat. This exposed Jake's human body to the toxic air, in time allowing Quaritch to subdue Jake. Intending to use Jake's own knife to cut his avatar's throat in a symbolic act of retribution for his betrayal, Quaritch's own life was ended by two arrows to the chest from Neytiri, who had taken the time to free herself during the struggle.
Corporal Lyle Wainfleet
Wainfleet in his AMP suit
During the final battle, Wainfleet in his AMP suit and many other RDA soldiers were overrun by stampeding hammerhead titanotheres, and in the process Wainfleet was trampled on and killed.
Tom Sully
Tom Sully was killed a week before shipping out to go to Pandora when a man killed him in an attempt to take his money. His death was the door to the events of the film, as Jake went to Pandora and replaced Tom in the Avatar Program.
Na'vi
Eytukan
He was killed when a shard of wood from the Hometree impaled him in the torso, during the RDA assault. Before succumbing to his wounds, he gave Neytiri his ceremonial bow.
Tsu'tey
Tsu'tey attacks a Scorpion gunship
After Jake was able to regain the trust of the Omaticaya by becoming the sixth Toruk Makto, Tsu'tey agreed to fly with him in the final battle against the RDA. Tsu'tey was gravely wounded in the fighting when he boarded the Valkyrie shuttle in an attempt to halt its bombing run. Though he killed several soldiers, shooting one with an arrow, striking several with his bow and even throwing some to the jungle below, he was shot multiple times by one of the remaining soldiers and fell from the shuttle. Tsu'tey survived the fall due to landing on several huge tree leaves before hitting the forest floor. As Tsu'tey lay dying, he passed his leadership onto Jake, who then ended Tsu'tey's life at his own request.
Other creatures
Seze
Seze, Neytiri's mountain banshee
Seze was Neytiri's mountain banshee. She was killed by an AMP suit controlled by Lyle Wainfleet, when Neytiri tried to evade a Samson in the final battle.