Are fighting types useful throughout the whole game, or just for the second gym? I seem to recall that they were awful in red/blue.
They are good, and there are plenty of really good ones (Sawk, Scrafty, Conkledurr, Mienshao and the trio) in BW. Generally, it's a good STAB and most Fighting types have access to lovely Close Combat. Pick any one of the before mentioned and you can't go wrong. It's basically choosing which secondary typing you'd prefer.