Don't know if anybody is still watching/reading this series, but it looks like it will be coming to it's epic conclusion soon. I think it's become really deep and interesting during shippuuden and I've become more engrossed in it. If anybody IS reading/watching it, some food for thought as to who Tobi is. Switch the words around a little and you have Obit, when pronounced in Japanese is Obito. Tobi only shows one eye, and we know what happened to Obito when he tried to save his team members including Kakashi.
Just a theory that my gf heard from another friend that is a fan.
Another theory is that it's Uchiha Shisui, but I don't think that holds up cause Itachi got one (which was implanted in one of his crows) and Danzou had one as well I think.