Are you looking for a second body (i.e. you'd continue to use the T2i alongside whatever you buy), or are you looking to upgrade? It matters, because the ergonomics and controls of the Rebel line are quite different from the higher end stuff - you'll soon find yourself reaching for the missing joystick or trying to spin the 4-button controller on the T2i, then realize it's not a quick control dial, and miss the shot. Ultimately, you will end up not using the Rebel much, if at all.
If you're looking for an upgrade, the 7D is the cream of the crop (cameras). AF is the best you'll find short of a 1-series. The 5DII does have better AF than a Rebel, but not a lot better.
The big con of the 5DIII is that it's not available now, and not for the near (and maybe far) future. Also, with a FF body, you would then lack a general purpose zoom for that body.
Either way, budget for new memory cards, too, since the 7D uses CF cards, not SD.
Ultimately, I think it comes down to what you shoot the most. If you shot a lot of action, sports, birds, wildlife, etc., the 7D is the way to go. If you shoot a lot of landscapes, portraits, macro, etc., the 5DII is better in general, although in your case you'd have to alter your lens collection to suit FF.