Many will probably disagree with me on this, and I have doubts about it myself, but I think that Tobi may NOT be Madara. I know that Tobi being Madara makes sense and no one else would fit the part (at least I can't think of anyone) but I just want to put these out there:

1) Tobi is just a mask. Any ninja powerful enough could put on a mask and carry out an attack and blame it on Madara. Uchiha Madara was an extremely powerful ninja, so it would make sense to anyone who knew how powerful he was. Another reason he could be pretending to be Madara is to make people fear him and cause the 5 Kages be too afraid to put Naruto and Bee out on the battlefield, which might be too much for Akatsuki to handle.

2) We haven't actually seen any of Madara's powers of weapons that were used in his fight with Hashirama. He says this is because he hasn't gained his full powers back yet, but that could easily be a lie. The only thing we have seen that suggests Tobi is Madara is a Sharingan, and he won't even toon his Mangekyo design.

3) When Tobi took off his mask for Kisame, Kisame bit off his tongue before anyone could see Tobi's face. Well we already know Tobi is Madara, so what's the big deal if we see him? Maybe Kisame was trying to protect Tobi/Madara's true identity. If u think about it, if Tobi really is Madara, there is no need for him to wear a mask anymore because everyone knows who he is.

4) Kabuto calls Tobi "Tobi" and then says "Sorry, u go door Madara these days". He then shows Tobi a coffin that apparently holds someone very powerful and can't be known to exist. He reassures Tobi that he hasn't told anyone yet. My theory- the 6th coffin is Madara.

Please commentaar and let me know what u think. I want to know if u think this could be plausible of if any of my theories have holes.