In no particular order...

Matrix Reloaded.... Neo takes on 30+ Agent Smiths... Absolutley jaw dropping every time!
Children of Men.... Army invade Immigrant Camp........ Intense, graphic, brilliantly cinematic and well sustained action!
Saving Private Ryan.... When the German Knifes the U.S Soldier....Thats it for me!
Paparatzi.... Cop first questions movie star..... Vey, very clever script. Cop lays an absolute minefield!
King Kong... When the dinosaurs stampeed..... I was just like WTF?!Slow and Horrifying

Honerable mention

Saving Private Ryan.... German Soldier digging himself two holes.... Clever metaphoric humor