A couple of noteworthy ones that came to mind.
1. The classic, cult film - To Live and Die in LA - Michael Mann film I believe (one reason I like it). Beginning of the film, when the agent is on Dafoe's property and digging through the large trash receptacle. One of Dafoe's thugs, armed with a shotgun, catches him unaware and with the drop on him. Unfortunately, the agent's life is ended quickly, and for once (for a Hollywood film) without any fanfare. Short, quick, brutal, and final. Just like real life. A "uber" tactical shotgun wasn't needed, or used, just what appeared to be a simple, run of the mill 12g. Tactics and awareness are the lessons here. Backup would've been nice also!
2. The Way of the Gun. I particularily liked the part in the hallway, where Benicio's character takes note of his adversary's foot extended just past the corner. He then procedes to shoot center mass of what his target has exposed, the foot. This leads to an easier finishing shot directly afterwards. Important lessons - For searcher/building clearer: Take in the WHOLE picture, not just chest/head height when scanning. Your adversary might be particularily crafty, and laying down, presenting an unusual situation. Remember, there are no rules. Also, when scanning, pay particular attention that your ready position doesn't block your vision/periphial vision of items that are lower. Lesson for stalker/lying in wait (actually, this is a lesson for anyone building clearing, or using cover): Pay attention that no portion of your body is leading around corners.
EricO