I’ve just discovered the excellent archive of war film on the website of the National Film Board of Canada. Plenty of the predictable stuff: soldiers marching, doing things in camp, etc. But some seemingly authentic battle footage and some interesting oddities like “German Atrocities in Cemeteries”, showing desecrated graves.
The film clips are backed up by historians’ essays, and there is an archive of stills, too,
You can find the archive by clicking here . Be warned, though, the films can take a long while to load.
Update 2011: The films and stills seem to have been deleted or moved to another location. I’d welcome any information from anyone who reckons they can still be found.