[Chronic Diarrhea]

There can't be THE most famous moment, because there are so many movie classics, but here are some off the top of my head:

Raiders of the Lost Ark: Indiana Jones swaps out the idol for a bag of sand, and then gets chased by a huge boulder.

Gone With the Wind: Although most on this board probably haven't seen the movie, it's still regarded as a true masterpiece. The first swear in a movie when Rhett Butler says to Scarlett O'Hara: "Frankly my dear, I don't give a damn," and the scene where he kisses her for the first time.

The Wizard of Oz: "Todo, we're not in Kansas anymore."

Jurrassic Park: The scene at the end where the T-Rex saves all the characters from the Velocaraptors, and then makes his battle cry as a banner which reads, "They ruled the Earth" flies down in front of him.

Star Wars: "I am your father."

Saving Private Ryan: It's still relatively new, but I think everybody can agree the D-Day scene will probably never be re-created as memorably as Spielberg made it.

Psycho: The shower scene.

Forrest Gump: "Life is like a box of chocolates, you never know what you're gonna get."

Now I'll list just a few that probably aren't regarded by many as great moments:

Schindler's List: The entire movie.

Full Metal Jacket: The opening Marine boot camp scene.

Sling Blade:
Doyle: "What are you doing with that lawnmower blade?"
Karl: "I reckon I aim to kill you with it."