If Craig Fairbrass (the guy who voiced Gaz and Ghost in Modern Warfare games) is to be believed, Infinity Ward may be working on a game starring the character Ghost.
Speaking at Modern Warfare 2 launch event in UK he said, “I’m now voicing a guy called Ghost, who now just got a spin-off comic of his own and they’re talking about another little game to go with it.” If what he says actually comes to fruition, we may actually have a spin-off of a spin-off on our hands!