I think i know who tobi is
It took me a long time but remember when tobi fought Konan to get the rinnegan. Yea, But konan was beating up tobi. tobi had to remove half of his mask to use the Izanagi . (Izanagi is the technique the danzo used against sasuke with all the sharingan on his arms) http://www.mangadaddy.com/naruto/510/4/
Wasswa, Now for the people who that Obito ur theory could be true because tobi has a sharingan on his right eye and the Izanagi on his left which means u had to inplant that in your eye. and obito lost his eye so it could b him.
But then the obito theory comes to a end becuz to use the the Izanagi u the powers of the uchina and the Senji. Now how Danzo used his Izanagi is becuz orochimaru gave him the power of senji by injecting him and he got the power of the uchina by the sharingan buyt however it was incomplete. So i cant be obito cause he doesnt have the power of the senji. hes still under that bolder lol. http://www.mangadaddy.com/naruto/510/10/
Now, the people who say its Shisui Uchiha could be right becuz once again when tobi fought Konan and she blew him up it showed tobi without a right arm. And Danzo took Shisui Uchiha right arm and he also have 1 sharingan becuz danzo took that to. http://www.mangadaddy.com/naruto/509/14/
Also Shisui Uchiha name means "Death by Water" and he died drowning leaving no corpses. hmmm
It cant be Izuna becuz he died in a battle and also suffered without having is eyes.
This answer is .................. Shisui Uchiha!! I have 3 reasons why is him
Shisui's name has two interpretable meanings. Combining the words Shi (死, Death) and Sui (水, Water), Shisui would mean "death water", which is a reference to his death by drowning. "Shisui" (止水) alone means "still water" or "stagnant water". Why would he chose to die by drowning when hes a master at water.
Second, Shisui Uchiha is the MASTER at the Body Flicker Technique. This technique is a high-speed movement technique, allowing a ninja to move short to long distances at an almost untraceable speed. To an observer, it appears as if the user has teleported. isnt this was Tobi does. Yes he does.
Third, Shisui Uchiha is Itachi mentor. they trained together, they were best friends. When tobi used the Body Flicker Technique itachi was the only who could see him moved at that speed since "they trained with each other" =)
Forth,When Ao fought Shisui, ao losted and said he will never forget him and chakra. When Danzo became the new hokage and went to the somit Ao could feel some shisui chakra in Danzo and also felt some from tobi .http://naruto.wikia.com/wiki/Ao read it will give all the info that Shisui Uchiha is tobi
Fifth, Danzo took one of his eyes and he also didn't have a right arm just like tobi. when sasuke killed danzo and tobi took danzo body so he can get the shisui eye, why u think he was so pissed. its becuz he wanted his eye back to release him full power
I like your detective work though! ;) But Itachi had the other Eye...."Tobi" Simply wanted the eye for Shisui for it's power...whom "Tobi" Is is a mystery for the moment...hopefully it'll be solved soon...mostly I hope he comes face to face with Madara....haha