Militaries have been major customers for space launch, in areas such as communications, remote sensing (Image Intelligence or IMINT), and intercepting enemy communications (Signal Intelligence or SIGINT). A nice overview of USA military launch needs (focusing on existing markets) is "Military Space Launch Vehicles" from the Federation of American Scientists. In particular this site is the best source I know of for information on mission models (expected future demand for launches) for the USA military (and at least to some extent intelligence agencies and NASA).
Using a suborbital vehicle for delivery of packages or people, for logistics or rapid deployment, is one potential new military market. Watch for smoke and mirrors, especially regarding rapid deployment--even subsonic aircraft cannot transport a sufficient payload to replace aircraft carriers, overseas bases, and other conventional approaches. Instead think of this market as similar to the civilian earth transport market--as a way to move things like important parts and Very Important Persons. This market was discussed in some detail by the US Air Force's Integrated Concept Team study from 1996 or 1997; what I know about this study is what is said in "USAF ICT Study", Space Access Update #72, published by the Space Access Society, 23 May 1997.
There are various other ideas for new military markets (e.g. weapons fired from space). One really good overview of weapons is the online report Space Weapons Earth Wars, Bob Preston, Dana J. Johnson, Sean Edwards, Jennifer Gross, Michael Miller, and Calvin Shipbaugh, RAND corporation, 2002.