Asuma Sarutobi killed by Hidan(Akatsuki Member).Hidan performed a jutsu that caused Asuma any damage that Hidan received. Knowing he himself wouldn't die, Hidan stabbed himself in the stomach, fatally wounding Asuma, and eventually leading to his death.
Chiyo Baasama killed by Herself.Akatsuki had extracted the one-tailed demon Shukaku from Gaara, causing him to die. Feeling guilty because she was the one who had sealed Shukaku in Gaara, Chiyo revives Gaara with a special jutsu. As a consequence of the jutsu, however, she was required to exchange her own life.
Deidera killed by Himself.Deidara is angry that it was Sasuke, and not him, who killed Orochimaru so he sets off to get revenge. As soon as he finds Sasuke, Deidara begins to attack Sasuke. Using his Sharingan, Sasuke is able to avoid most of Deidara's attacks. Frustrated that he is unable to defeat Sasuke,he exploded himself hoping to get sasuke along with him but sasuke summoned manda and the explosion only killed manda
Dosu Kinuta killed by Gaara. Details: Dosu tried to sneak up on Gaara to kill him so that he could have a higher chance of fighting Sasuke in the Chuunin Exam to prove to Orochimaru his worthiness.Too bad for him that Gaara was to strong
Gaara killed by Deidera(Akatsuki Member).Akatsuki wanted the one-tailed demon Shukaku in Gaara, so they extracted it out of him. As a result Shukaku's extraction, Gaara died and was brought back to life by chiyo.
Gato killed by Zabuza:Gato betrays Zabuza and threatens to kill him for failing, so Zabuza kills him first
Haku killed by Kakashi.Kakashi set up his chidori in attempt to kill zabuza.Haku jumped in is way and was killed.
Hayate Gekko killed by Baki.After finding out that the Sound and Sand Villages were conspiring against the Leaf Village, Baki chased Hayate and killed him before he could warn the other villagers.
Hidan killed by Shikamaru.As revenge for killing Asuma, Shikamaru lures Hidan to the Naara ranch, and trick him into falling in a pit. With Hidan surrounded by explosive tags, Shikamaru throws a cigarette at an explosive tags, causing them to detonate, and killing Hidan.
3rd Hokage killed by Himself/Death God. In a long and hard fought battle during Orochimaru's invasion of the Leaf Village, the Third Hokage used a jutsu to seal the soul of Orochimaru's arms, inside his own soul, which was taken by a death god.
4th Hokage killed by Himself/Death God. In order to stop the Nine-Tailed Demon fox from terrorizing the Leaf Village, the Fourth used a jutsu to seal the Fox in his son Naruto, and having his soul taken away by a death god (not shown in anime/manga, but implied by Third Hokage during his battle with Orochimaru).
Uchiha Itachi killed by Himself/Sasuke: Details: Itachi went all out against Sasuke to take his eyes so that he could have the Eternal Mangenkyo Sharingan. Sasuke inflicted several major blows on Itachi, and combined with the damage and chakra drainage Itachi's Mangekyo Sharingan attacks caused himself, Itachi fell to the ground, flicking Sasuke's head (like he did when Sasuke was younger) and transfered his eye techniques in sasuke's eyes and died.
Jiraiya killed by Pain(Akatsuki Leader).After finding a lead on the Akatsuki Leader, Jiraiya goes to the Hidden Rain Village to investigate. There, Jiraiya finds out the Akatsuki Leader calls himself Pain, and is actually a former student of Jiraiya - Nagato. Jiraiya tries to convince Pain that Akatsuki is a terrible organization, but he doesn't listen. The two engage in battle and in the end jiraiya was killed.
Kakuzu killed by Kaakshi/Naruto:Naruto uses his new attack, the Fuuton: RasenShuriken, damaging Kakuzu at a cellular level, severing all of his nerves, destroying 2 of his hearts, and bringing his last heart to the brink of failure. With Kakuzu unable to move, and Naruto injured himself as a result of his own attack, Kakashi walks up and finishes Kakuzu off.
Orochimaru killed by Sasuke/Itachi:It's almost been three years and Orochimaru's body begins to fail him so he starts to think about taking over Sasuke. Before he has the chance though, Sasuke, jumps in to try and kill him. Orochimaru turns into his real form, a snake, and begins to suddenly transfer himself into Sasuke. With the use of his Sharingan, however, Sasuke turns the tables and takes over Orochimaru instead and absorbs him. At some time period later on in the Naruto series, Itachi and Sasuke fight. With Sasuke's chakra extremely low, Orochimaru pops out of Sasuke to get to Itachi, but is instead, hit by Itachi's sword "Totsuka" which traps Orochimaru in a dream-like genjutsu for all eternity.
Sasori killed by Sakura/Chiyo:Sasori fought with Sakura and his grandmother, Chiyo while Naruto and Kakashi went after Deidara to rescue Gaara. After a long, hard fought battle, Sasori was eventually stabbed in his heart using the Mother and Father puppets by Chiyo.
Zabuza Momoichi killed by Kakashi/Gato's Men:To defend Gato. Zabuza was already heavily injured from his battle with Kakashi, but Gato's men stabbed him with their weapons as Zabuza dashed to kill Gato. Zabuza succeeds in killing Gato, but also ends up dieing himself.