special pricing by address

I am trying to get started with a new site. I am trying to come up with a way to do special pricing. I already have an idea of how to get the addresses (there would be quite a few), but I don't know how to get them to apply a discount. I was thinking of getting the addresses into a list which could be accessed by entering a zip code and selecting one that comes up rather than using dropdown menus. I want to have it apply a discount if a qualifying address is used. This would be something along the lines of the military discount which could be done with a download I saw on one of these sites that applies a discount if the shipping address is FPO or APO, but would apply to addresses that would not be as obvious. Any help would be appreciated.