American Civil War: Cold Mountain, Gettysburg

American West: Tombstone, Dances with Wolves

World War I: All Quiet on the Western Front, Warhorse, Joyeux Noël

World War II: Saving Private Ryan, The Longest Day, Tora, Tora, Tora!, Das Boot

Vietnam: Platoon, Full Metal Jacket

Ancient Rome: Spartacus, The Eagle, HBO's Rome (it's not a movie but an extended miniseries, it's too amazing to leave off), Ben-Hur, Warrior Queen (Boudicca)

Middle Ages: A Lion in Winter, Henry V, Black Death, Braveheart, The Seventh Seal, King Arthur

(I'll add more later but I can't say how historically accurate they all are)