Gallipoli was a good movie regarding the first world war but its limited in scope. WW I was a pretty harrowing war with chemical warfare in use etc.. The Battle of the Somme being bloodiest battle ever recorded. I think a good WW I flick could do well.
The Lost Battalion http://www.youtube.com/watch?v=HLhasKqP3Yw All Quiet on the Western Front There's also a number of movies made around the aircraft flyers of the age.
not a movie, but probably the best account on WWI ever written. Ernst junger, one of germany's most decorated soldiers, served as a germany army officer, wounded 14 times in combat, gives a very harrowing account of trench warfare, the insane infantry charges, night commando operations. Remarkably, he lived till 102 yrs old. http://www.amazon.com/Storm-Steel-P...=sr_1_1?ie=UTF8&s=books&qid=1269875738&sr=1-1
Great book: "Eleventh Month, Eleventh Day, Eleventh Hour: Armistice Day, 1918, World War I and Its Violent Climax" http://www.amazon.com/Eleventh-Month-Day-Hour-Armistice/dp/0375508252