What was in this coffin ?! There are two big schools of thoughts on this that we identified: Tobi is Madara, or Tobi is not Madara
If Toby is Madara then Madara's body can NOT be in that coffin. And It cannot be Chuck Norris

!!!!!! (You people need to think a little more before throwing bad jokes.... I mean seriously, Chuck Norris would need to be dead.... pfffff not up in here !!!!!!!!) Could be Madara's boyfriend

?! (alright enought with the jokes)
I wouldn't know who's in that coffin if tobi IS Madara cause I don't know who Madara would not want the people to know is dead.
Could it be Minato? Why the heck not? We could simply explain that Orochimaru's summoning failed against the 3rd because his soul was still inside Naruto (And thus not because of the thirds' counter attack) but Minato's soul is now out of Naruto's body making it possible to summon him now. Could be Minato, for all I know Tobi was really surprised when he fought against him.
But then why would Tobi want to keep it a secret from other people? (as implied by Kabuto?) For this very same reason I don't think that inside the coffin lies:
the first, the second, third, Jiraiya, his brother etc.... Maybe inside the coffin is someone that we (and ultimately Madara) think is still alive but is deceiving everyone.
Let me explain that last statement:
What if inside the coffin lies Zetsu.... Then who da hell is the Zetsu acting under Madara's orders?! It doesn't have to be Zetsu, but could be any one close to madara, that he would trust. And it would make sense that this information must not be known.
But then again why would Madara submit to Kabuto's deal when he already knows who among his "friends" or ally is dead.
If Tobi is not Madara then it's definately Madara in that Coffin:
From that point the real question becomes who is Tobi.
-Obito: When he is crushed he says his right side is "probably" crushed but he can't feel it. Would fit if at this point he is unknowingly using his sharingan's time/dimensional capacity. People need to give credit to this Theory, but WHY would Obito turn evil.... Well Sasuke turned Evil out of nowhere too so who knows... (I mean Sasuke was a little evil to begin with, but the way he is know is just way out of hands...)
-Madara's Brother: After Madara's death against the first hokage, the brother could only retreive one EMS, the other one being destroyed during the fight, or maybe he has both EMS, just only uses it for great occasions. (Naturally the same would go if Tobi is Madara, and that he has both EMS)
-I don't think that Tobi is Shisui for a couple reasons:
Shisui was killed by Itachi Uchiha so that he can awaken his MS (by far the coolest Uchiha of them all by the way)
Shisui's right eye was in Danzo's right eye lob. (We only get to see Tobi's right eye...)
Shisui's sharingan's power is to convince people make them think what ever the user wants to (inception

), not traveling throught dimension and time. (But then to think about it, Tobi is really good at convincing people..)