after commuting for a while, I think that probably the best bike for a commute would be an aluminum SS mountain bike (w/rigid fork). something like that would not be hurt by salty roads, rain or grit a whole lot. I would choose drop bars for a longer, less-traffiked commute, and flat bars for a more city-like commute. I would probably want rhyno lites with a fairly fat slick that wouldn't puncture too easily. v-brakes front and rear, I say this becuase disks are too flashy, and i think would get ripped off too easily.

of course this all depends on the circunstances of your commute. if you can change your clothes, I'd go without fenders, mostly becuase they limit your tire size, and they dont look cool. if you ride in the dark a lot, I'd get a light, but not a hub generator type of light, just becuase they are really expensive. if your commute is over 5-6 miles, i'd go with a trunk rack instead of a backpack. shorter that though, a backpack is fine.