Battle of James Island from the 1989 film Glory
Glory is the film that basically had me fall in love with Civil War History specifically and military history in general and while the opening Battle of Antietam and the climatic Battle of Fort Wagner were far more epic, it was the Battle of James Island (which was comparatively more like a skirmish cinematically and historically) which was my favorite part of the film. Looking back on it now there's some problems with the battle scene that seemed to of been missed in the editing room, but overall I love the rush into battle and the passage between the fleeing Union troops and resulting Cavalry charge (which isn't shown in the above clip) as well as the volley trading before the final decisive clash into melee. Like Braveheart with muskets.
Plus you get to see Ferris Bueller all grown up and leading Denzel Washington, Morgan Freeman, Andre Braugher and Westley into battle!!!