Propaganda posters of WWI:
http://www.firstworldwar.com/posters/index.htm
Nazi posters from 1933 to 1945:
http://www.calvin.edu/academic/cas/gpa/posters2.htm
American posters of WWI:
http://www.library.georgetown.edu/de...l/amposter.htm
Russian propaganda posters (you can actually buy these from the online shop):
http://posters.nce.buttobi.net/
World War II posters collection:
http://www.library.northwestern.edu/.../wwii-posters/
World War 2 posters (lots of great links here):
http://www.ww2poster.co.uk/
Posters from the Great War:
http://www.worldwar1.com/posters.htm
Have fun.
Mr Mephisto
PS - Google is your friend...