Re: Tobi theory..
I also believe that Tobi and Madara are one and the same.
Tobi had knowledge of Madara awakening the Rinnegan, he kept saying 'I was the second sage of the 6 paths.' He called Nagato the 3rd. It only makes sense he was referring to the Rinnegan, since Nagato didn't have DNA transplants, so was not the younger and elder son combined.
He also claimed that Nagato's Rinnegan used to be his. Nagato never being shown with eyes other than Rinnegan lends support here, since transplanted dojutsu tend to remain in an active state.
Tobi claimed to have given the Rinnegan to Nagato.
Madara mentions Nagato upon ressurection, so met him either before death, or through a failed resurrection by Nagato.
In short Tobi had access to a fount of information that only should have been available to Madara.
My theory goes something like:
Having awakened the Rinnegan shortly before his death he realized he had neither the vitality, nor the power to realize his goal, which was to become the second sage of the six paths, and bring peace to the shinobi world. Madara cloned himself into a body fashioned from the first hokage's cells. He used a shikki fuin to create a strong, lasting seal on the fashioned body. This was doubly effective, as it caused his body to remain in a youthful state, while allowing his will to live on.
His clone had instructions to take his eyes and pass them onto someone youthful, so they would have plenty of time to grow into their powers and be capable of resurrecting him.
He furthermore was to go about collecting the tailed beasts so that the juubi was usable when Madara would be revived.
To aid his clone and ensure his survival he was given three powers: immaterialism, and teleportation through the Rinnegan, and a sharingan to control tailed beasts and people.
Tobi is nothing more than a Madara jinchuriki, once the chakras that have been sealed into him get used up he will fade just like Minato did from Naruto. Minato sealed his ability to control tailed beasts and people, so all he has left are the immaterialism and telportation. Luckily these are generic jutsus, and can be used with the chakras generated from the fashioned body.
A lot of this has been stolen from other people's theories, there are a few additions of my own though.