Check out Topo Zone (http://www.topozone.com/)
They have a bunch of free maps. You can search specific areas, or you can just find a sheet that has some good terrain.
You can sign up and pay for downloads ($50), or I think you can sign up and demo it and get some downloads. Otherwise, you can search and shift around the map sheets without registering, but you can't zoom out or do some other manipulations to the map. All else fails, just hit "Print Screen", paste it into Paint or PowerPoint, crop and re-size as needed.
The only easily searchable military installations that are on the site are Canadian. If you can get your hands on a paper 1:50,000 from the USGS, get the sheet for Ft. Lewis, Washington. The sheet is a good all-around training map, and it contains (I think) every major and minor terrain feature that you get taught for Land Nav. If I remember correctly, it's the Tacoma map sheet. You can order map sheets from USGS at http://store.usgs.gov/
I'd also reccomend checking out GoogleEarth. It's a nice resource that gives you sat photos of the world. Such free, high resolution photos are used by personnel on deployment sometimes since the stuff is readily accessible, of pretty decent quality, and because the most popular viewed areas (such as areas of conflict) are updated more frequently, so they are fairly current. It's also popular with our enemies too: a tool of the modern age which gives a non-state actor capabilities that only rich nations posseessed less that 10 yrs ago.
Gotta love technology.