Firebats work much better than people think. If you build enough firebats at the beggining of the game, you really dont even need bunkers (atleast not yet). But don't get me wrong, they get slaughtered on their own. Combine them with marines and medics. For example, when you get hit with a bunch of Hydralisks, chances are your marines will buy time for your firebats to get up close and personal. Once in close range, they will make quick work of the Hydras. Even if they get butchered before they make it, thats less damage your marines had to absorb (who die much faster than firebats). Here is another great tip - Because Archons are mostly shield, Firebats can do full damage. Both units are close range, and firebats cost half as much and build four times as fast. Having a nice group of firebats around will make quick work of small groups of Archons when you dont have EMP. Always use Firebats against the zerg.

CreepColony's Opinion: I disagree that Firebats are good against Hydras because they don't do much damage and will die quickly. I don't think they're too good against archons either, since firebats are small and they will be hit easily with splash damage. Tanks and vultures (their grenades, not mines) are also good against archons.