I've seen quite a few 'war' movies, and I've always wondered which movie portrayed an actual fire-fight the best. Now I've read that no two combat engagements are ever the same, but I seriously doubt that the John Wayne World War II movies showed combat as it usually is.
My vote goes to the Vietnam era fire-fight in "Forrest Gump". Gump's platoon is marching through a rice paddy, with a tree line a few hundred yards ahead of them. Suddenly fifteen or twenty 'twinkling' muzzle flashes can be seen in the jungle and green tracers start zooming by. You can't see any actual VC or NVA, just the muzzle flashes. Somehow the VC or NVA manage to fire a mortar from the jungle and it starts bracketing the platoon (which are hiding behind a rice paddy dike).
However, after this point in the movie, things get a little bit 'creative'. But, I think this first half of the fight is realistic.
From the first person accounts I have read, this seems to be the most 'probable' form of a fire-fight that could be depicted in a movie.