Advances in military technology trickle down to civilian life all the time. Radar, computers, jet engines, satellites, the list goes on. (Oh, and the Internet, which I already mentioned below.) Battlefield medicine has made huge advances too, which are applicable to injuries that have nothing to do with warfare. The big area where I think there has been too little transfer is rocketry, where federal regulations severely restrict employment and the availability of technology.
I don't view any of this as an actual justification for military spending - I'm firmly in the camp that believes the US should be like Switzerland with nukes. But it's simply ignorant of history to claim that military research never benefits anyone but the military.