The CIA heist that named and codified the "Mission: Impossible" Cable Drop, showing that an intense scene in a summer blockbuster can be done without explosions and body count, rather with an emphasis on silence and tension.
Ethan's escape from Kittridge; as soon as he figures out the mission was a mole hunt with him suspect number one, he just keeps the man talking until he blows up the fishtank as a distraction, causing him to outrun a wall of water.
Having lost almost his entire team and been framed as The Mole within the IMF, how does Ethan turn the entire situation around? He goes straight to his primary target "Max" and charms her into accepting his help by basically telling the truth and fooling her into thinking he has switched sides for real. Not only was he able to uncover the extremely elusive Max's true identity, but he was able to convince her to set up a meeting with "Job", the actual IMF traitor.
The climax definitely deserves a mention, but it wouldn't be complete without the music. Until this point, the music has been this cacophony of instruments as the train sequence plays out, showcasing the chaos and danger of the situation. But when Kreiger nearly loses control of the helicopter before he can slice Ethan's head off, the music does the equivalent of a, "CHARGE!!!" and then blows out the M:I Theme crystal clear in a different key, a musical equivalent of, "And the fight is on!" The sequence is so Rule of Cool that even Roger Ebert admits in his review even though there's no plausible way a chopper could fit inside the Chunnel and have room to maneuver, it looks so damn awesome that you simply let it go.
Let's not forget the scene immediately preceding the fight atop the train. Ethan ruins Phelps's entire plan with just a pair of glasses. "Good morning, Mr. Phelps," indeed!
Ethan: I'm not the only one who's seen you alive. Jim:You... son of a bitch! Ethan: It's over, Jim.
