I always seem to have trouble against Zerg as Terran, but ESPECIALLY if there are a mass of early Mutas harrasing me. I know Marines are great against them but that's not good enough, because they aren't as mobile as the Mutas and unless that's their only unit I can't really just rely on the amount of Marines it would take as I need to build other units. However Vikings I've realized pretty much suck against Mutas as far as I can tell. I heard Thors are good but that's not reasonable for early game.

Anyone?