This page from the Pentagon Library has a long list of resources. And this similar page from the HQ Dept. of the Army contains not only clip art, but PowerPoint templates and other presentation tools.
The Ad*Access Project, funded by the Duke Endowment "Library 2000" Fund, presents images and database information for over 7,000 advertisements printed in U.S. and Canadian newspapers
and magazines between 1911 and 1955. There is a special category for World War
II with many well-known and obscure ads from that period.
Animation Factory has many
military GIFs in their index. Try War, then Transportation for planes and helicopters,
Flags for military flags, and Misc. which has sub-headings for Cannons and Guns,
Army Awards has a "Rack Builder" listing of images of US Military Decorations, Good Condust, Service (Campaign) Medals and Service and Training Ribbons, and more.
Digital Vector Maps sells royalty-free downloadable and editable digital maps in Adobe Illustrator or PDF format. All maps have fully-editable layers, graphics and text. Their wide selection includes blank and high-detail world maps, US and other country maps, individual US state maps and specialized maps such as the Arctic National Wildlife Refuge (ANWR). Order on-line and download instantly.
The Federal Clip Art Collection is electronic artwork illustrated on a computer by expertly trained artists for
use by desktop publishers competing in the federal arena. Federal Clip Art has
14 collections of over 7,800 computer illustrations hand-drawn to government
specifications. Topics range from military insignia and combat art to foreign
and domestic maps, flags and coats of arms.
WallpaperSuggest.com has a big collection of Military Wallpaper for your computer screen. Many other topics are available as well.
Find More Information on the Internet
There are many fine websites that have additional information on this
topic, too many to list here and too many to keep up with as they come and go.
Use this Google web search form to get an up to date report of what's out there.
For good results, try entering this: military clipart or posters. Then click the Search button.