Ok, so not that things are coming to a head between Naruto and Tobi and their fight, I feel we will know the true identity of Tobi soon enough. Before that though, I'd like to post my theory on who Tobi actually is, I've had this theory since the Shinobi war started. I'll put it in another spoiler for those that don't want to know yet.
Spoiler For Spoiler:
Real short, Tobi is Obito Uchiha. Primarily, we see that the side of his mask without the eye hole is the same eye that Obito gave to Kakashi. Beyond the obvious similarity with hair, Uchiha, and similar name, there is one thing that utterly confirms this for me. Tobi has similar jutsu dealing with manipulating space/time as Kakashi can launch with his sharingan. We know from previous references that each individual Uchiha can have jutsu's unique to his or her sharingan. We even see in the latest episode that Tobi actually stopped Kakashi's jutsu, nullifying it with the same power.
There is also a small teaser in the last chapter. When Kakashi demanded for Tobi to remove his mask, he replied, "You don't remember faces well anyways" Implying that Tobi and Kakashi knew eachother.
Kinda spitballed together, but I wanted to say that somewhere before we actually know for sure