Tobi
Tobi was formally Zetsu's subordinate. He has a very formal and correct manner of speech and wanted to fill in Sasori's position in Akatsuki after he had died. To his luck, he was eventually let in Akatsuki. In chapter 362 Deidara blew himself up and it was believed Tobi died as well. In chapter 363, however, a surprising turn of events takes place - Tobi is seen giving orders to Pain! It is revealed that he is Madara Uchiha, the real leader of Akatsuki, and one of the founders of the Hidden Leaf Village. Madara created Akatsuki as a means to hide himself from the world, using their activities to disguise his own plans. As Madara, Tobi's personality and speech become completely different, with a much less formal speech and a more typically villainous sway. Tobi's only known abilities are that he can let attacks pass through him easily, and that he has the power of the Sharingan.
Pain
Pain is the assigned leader of Akatsuki, and is partners with Konan. He was told by Tobi/Madara to capture Naruto, and that because he is the leader, he cannot fail. Pain has shown us that he has as six different bodies which share the same mind, and are known collectively as The Six Paths of Pain. These bodies all have brown/orange hair color, piercing, and the Rinnegan doujutsu (which allows the user to perform any jutsu and manipulate all six types of chakra-nature manipulation). All six bodies are, in a sense, connected since they can share visual information seamlessly, giving Pain the ability to coordinate offense and defense of all six bodies as if they were a single entity.
Each of the six entities that are Pain were ninja that Jiraiya encountered as he wandered the world. Some of the abilities we've seen Pain's bodies perform are detecting the movements and chakra levels of people traveling within the rain (that he has created), the summoning jutsu, ability to absorb ninjutsu as a form of defense and the ability to fire his left arm like a missile.
Pain's real name is Nagato, and he was left orphaned by one of the Hidden Rain Village's many wars in his childhood along with Konan (who is also a Akatsuki member), and a boy named Yahiko (who is presumed dead). After one of the wars, Jiraiya met the three kids, and became their teacher for a short time. Sometime after Jiraiya left, Nagato started to view himself as a god destined to teach the world the meaninglessness of fighting. Eventually 'Pain' came into existence and single-handedly killed the Hidden Rain Village's former leader, Hanzo and those affiliated with him, and became somebody the village's people worship.
Uchiha Itachi
Killed everyone in his clan except for his little brother, Sasuke. Initially, Itachi murdered his best friend, Shisui Uchiha, to gain the Mangekyo Sharingan, but went on to massacre the rest of the clan, leaving only Sasuke. Seven or eight years after the Uchiha massacre, Itachi reveals to Sasuke that he had the help of Madara Uchiha, and the only reason he left Sasuke alive was to steal his eyes. The Mangekyo Sharingan brings upon blindness to the user, and the only way to prevent going blind was to take the eyes of one's sibling. With that goal in mind Sasuke was left alive to live hating Itachi, and one day possibly awaken the Mangenkyo Sharingan. At some point in time Itachi joined Akatsuki. The timeline that has been given throughout the series coupled with his age suggests that he joined the organization prior to killing his clan.
Itachi is a genjutsu specialist, and can trap opponents within an illusion by merely pointing or looking at them. He also relies heavily on his Sharingan in battle, and uses them to reads an opponent's movements and respond accordingly. With his Mangekyo Sharingan, Itachi uses the attack Tsukuyomi to take his opponent's mind into an alternate dimension and torture them. A matter of seconds in the real world is equivalent to hours to the person under control of Itachi's Tsukuyomi. The Mangekyo Sharingan is more than just genjutsu, however. There is a physical attack associated with it - Amaterasu - a ninjutsu, which emits a black flame several times hotter than the sun's heat. Both the Tsukuyomi and Amaterasu take up an incredible amount of chakra, so Itachi tries to wrap up battles as fast as possible.
Hoshikage Kisame
Kisame is one of the Seven Swordsmen of the Mist, seven powerful ninja who utilize large and unique swords. He has unimaginable amounts of chakra and wield's a sword called Samehada, which is a scale-covered sword that shaves things, instead of cutting them. It also has the ability to absorb chakra and prevent anybody other than Kisame to use it.
Unlike most members of Akatsuki who fight with one another, Kisame gets along well with Itachi. He listens to what Itachi says and looks out for him, indicating he ha a human heart. Oddly enough, Kisame has a distinctive shark-like appearance, as he has pale blue skin, small white eyes, gill-like facial structures, and sharp triangular teeth.
Like others from the Hidden Mist Village, Kisame uses water element jutsu in combination with his powerful physical attacks. Even if there is no water source where he is fighting, Kisame can use a Water Release Jutsu to create a lake's worth of water to aid him in battle.
Zetsu
Zetsu seems to have a split personality, as half of him is black and the other is white. The black half of his face speaks in a deep voice while the white side in a lighter voice. The two halves are often seem to talk to one another other and occasionally differ in opinion. This split personality might be the reason Zetsu does not have a partner. Along with having a "two-face," Zetsu's head is surrounded by what looks like a venus flytrap.Zetsu has the ability to merge the ground, trees, and other plants, which helps him immensely in his functions as a spy for Akatsuki. He also eats the bodies of people Akatsuki does not want found, such as spies and Akatsuki members who have been killed.
Konan
This is the only female member of Akatsuki. In chapter 363 we finds out that she is Pain's partner. Konan has blue hair with a white flower in it. When she was younger, Konan and her teammates (Nagato, and Yahiko) were left orphaned by one of the Rain Village's many wars, forcing them to fend for themselves. One day, they met Jiraiya, who stayed with them for a short while and taught them the art of being a ninja. Konan has a unique ability where she can divide her body into a countless pieces of paper. This paper can be controlled individually and formed into various shapes for a number of purposes, such as butterflies for scouting or random weapons for attack. Her weakness is water, as when she uses her paper abilities, the paper clings to itself and loses its stiffness.
Former Members
Kakuzu
Kakuzu is the tallest member of Akatsuki. He is obsessed about money, and will do anything to get it. He also dislikes Hidan's religion as he believes that the rituals Hidan performs are a waste of time. He gets in frequent arguments with Hidan because they have two distinct personalities - Hidan is a religious type of guy, while Kakuzu is a money man. The only reason Kakuzu puts up with it all because be believes in the end it can bring him money. Kakuzu was heavily wounded by Naruto using the Fuuton Rasenshuriken and then killed by Kakashi.
Hidan
Hidan is first shown with a three-bladed scythe and says that he is the slowest attacker in Akatsuki.. He was a very religious individual and prays to his chain of prayer beads before a fight, wishing for nothing less than a kill. He believed in the Jashin (wicked heart) religion where killing is encouraged and anything less than that is considered a sin. He put his religon into practice by killing Asuma. Unfortunately for him, Shikamaru could never forgive him for that and killed Hidan using explosive tags.
Deidera
A fancy and skillful fighter, with special mouths in the palm of each hand, he is able to manipulate clay into either a flight-capable clay bird that can support him or a a huge bomb that is capable of leveling a village without the use of exploding tags. After Sasori's death Deidara was partnered with the newest member of Akatsuki, Tobi. The partnership didn't last long as Deidara blew himself up as his final work of art to try and kill Sasuke.
Sasori
Flashbacks seem to indicate that his descent into darkness started when his parents died. Sasori is a very skilled a puppet master and controls puppets in combat. He can even turn the living into puppets and than use their jutsus. After killing Gaara with the help of his former partner Deidara, he fought with Sakura and his grandmother, Chiyo. They had a fierce battle, and in the end Sasori was killed.
Orochimaru