There's so many, but here's few of my favorites. Some of them are more of war-scenes than fight-scenes though, but war's fighting, right?
Matrix, the lobby scene.
Swordfish, well not actually a fighting scene, but the one where the bomb goes off + the car chase.
Saving Private Ryan, D-day.
South Park movie, the scene where Bill Gates is shot.
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Crouching Tiger, Hidden Dragon, the tree top fight.
Ghost in the Shell, the museum scene
Raiders of the Lost Ark, the one where Indy shoots the swordsman.
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LotR, the battle of Emyn Muil
Braveheart, all big battles
Star Wars ep. II, Obi-Wan+Anakin+Yoda vs. Dooku.