"Chuck! Chuck! It's your cousin Marvin! Marvin Berry! You know that new sound you were looking for? Well listen to this!"
In fact the exact moment when Marty is alive again as his father kisses his mother and ensures eveyone's future, thus causing Marty to instantly return to playing the song "Earth Angel" is easily one of the most triumphant moments in cinema, ever.
And the fact that when Biff threatens George and tells him to close the car door and walk away, George, in spite of being bullied by Biff the whole movie, stands his ground and says "No, Biff. You leave her alone." That line wasn't fed to him by Marty. That moment was all George.
After working so hard to connect the cables on the clock, the bottom cable suddenly pops free — and there's only a minute to go. Doc despairs for a moment, then gets a determined look. He reconnects the bits he has, then LOOPS THEM AROUND THE HANDS OF THE CLOCK AND SLIDES DOWN, retrieving the other end and connecting it JUST AS THE LIGHTNING BOLT HITS. Awesome.
Let's face it, there's a reason this scene is in all three films.
How can we forget "Roads? Where we're going, we don't need... roads." The line is awesome enough, but when you consider that the Doc has turned a Time Machine that he invented into a flying car AS WELL?
In fact, this line was so cool that Reagan incorporated it into his State of the Union address that year. He was a fan of the movies; when Doc disbelieves that an actor could be President, Reagan had the White House projectionist rewind and play the line again.
"The way I see it, if you're gonna build a time machine into a car, why not do it with some style?"
Marty's fight with Biff, and the chase scene afterwards. It ends with Marty avoiding getting crushed between a truck and Biff's '46 Impala by running up the hood, through the car seats, and off the trunk, with Biff and his gang getting buried in manure.
And to cap it off, he gets back on his makeshift skateboard just as it comes back out from under the car. AWESOME.
Real-Life Example: One of the execs wanted to change the name to "Spaceman from Pluto" due to the comic book that the kids on the farm are reading when Marty first makes it to 1955, thinking that no one would get the title Back to the Future (it doesn't take a genius to figure out the Fridge Logic there). The writers were stuck and really couldn't say anything, but Steven Spielberg on the other hand said this at a meeting: "We got the joke you sent us, it was hilarious." The uproarious laughter pretty much squashed the idea.
Sort of a combined one for Doc and Marty. Marty, faced with a gun by the 1985-A version of Biff Tannen, steps off the roof of the Pleasure Paradise. Biff walks forward slowly, muttering "Idiot." Cue Marty rising up, standing on the hood of the DeLorean, and Doc opening his door just in time to whack Biff in the face with it. "Nice shot, Doc" indeed!
Speaking of 1985-A, the moment Biff pulled out the gun after explaining to Marty how he got the Almanac. He may be a sleezey ass, but he can sure pull off an Oh Crap moment.
Back in 1955, after Marty realizes he's just followed a false trail and gotten nothing but Biff's dirty magazine.
Doc Brown: Marty, the entire future depends on you finding Biff and getting that book back!
Marty: I know! I just don't know where...
[Sounds of Biff and George's fight in the parking lot from Part I]
Marty: OF COURSE!!!
And this time he actually got to see his dad deck Biff!
The scene in which Marty surreptitiously makes his way to the stage and climbs the ladder onto the rigging, to drop the sandbags on Biff's goons to prevent his past self from being beaten up and the universe from being destroyed.
Biff crashing into the manure truck for the second time.
After all the trouble it's caused him and a long struggle to get it back, Marty finally retrieves the almanac and torches it, thus fixing the future and saving his dad.
When Marty McFly finally overcomes his Berserk Button and decides not to fight Buford Tannen over being called a 'chicken' — because, in Marty's words, "He's an asshole! I don't care what Tannen says. And I don't care what anybody else says, either!"
The best part being that Marty hits Tannen so hard, he stops and restarts the dramatic music several times before laying him flat out.
Doc shooting Marty down from Buford's attempt to hang him with his telescopic rifle definitely qualifies. "It'll shoot the fleas off a dog's back at 500 yards, Tannen — and it's pointed straight at your head!"
Face it, the whole scene. Doc stands up to Tannen's bluster and threats without flinching once, and throws his demands for payment back in his face standing like a Bad Ass with a huge ass gun.
Marty returns the favor for the above later by preventing Buford from shooting him. Not only was it a frisbee throw (using an actual Frisbee pie plate!), but he hit Buford's hand just as he pulled the trigger, and the only casualty was Doc's hat.
And there's also the fact that he shows up at the end of the movie in a TIME-TRAVELING FLYING STEAM TRAIN. Let's face it - Doc'sCOOL.
In Episode 3, the moment Citizen Brown realizes that the logo for the "new" Hill Valley is modeled after the flux capacitor.
In Episode 4, Marty is inspired to try and unbrainwash Jennifer by playing his guitar over the squawkbox, when a guard comes to escort her out and notices the music. When the guard inspects the camera, Jennifer beans him with her box of spray paints.
Jennifer: Nobody scrambles my brains, ya hear me?! No one! I'm Jennifer Parker - rock 'n roller!
Marty rescuing Doc in Episode 4 also qualifies.
Telltale got Michael J. Fox to voice a character for the finale. YES!
Correction, Fox did FOUR characters, including three Alt!Martys!
A slightly fridgey one in Episode 5. Citizen Brown is disguised as the runner of the Enlightenment Under The Sea attraction, and has his younger self kidnapped and hidden in the bathysphere. Marty knows this, and is trying to thwart him. He tries to get onto the ride with a ticket, then invokes the authorities when Brown rejects it. After all that, Brown pretends the gears are jammed so he can't raise the bathysphere. So what does Marty do? He deliberately crimps the bathysphere's air hose, cutting off young Emmett's air supply and putting his life— and by extension his older self's life— in jeopardy. He does this knowing full well that if Emmett dies, not only will he lose a lifelong friend, but he'll prevent the invention of the time machine in the first place (because its inventor won't be alive to invent it) and be forever stranded 55 years in the past. He's taking a MASSIVE chance, and he takes it without hesitation. Badass to say the very least.
He probably realized that the only one who cares about Emmett more than he does is Emmett himself. A difficult, but logically sound, decision.
When Young Emmett is showcasing his Electrokinetic Levitator at the expo, he rolls off the ramp, supposedly falling to the "spectacular failure" he mentioned in Episode 1... until he flies back into the shot, soaring majestically around the room. Made even more awesome by the accompanying triumphant version of the Back To The Future theme
William Mc Fly saving Marty and Doc from a trigger-happy Edna.
YMMMV on this, but how about having a single movie make twounknowns into household names as well as solidifying their careers in Hollywood for decades to come literally overnight?