When Arthur is firing his assault rifle at the invading mooks, Eames pushes him aside, tells him "You mustn't be afraid to dream a little bigger, darling.", and pulls out a multi-shot grenade launcher and blows them all away.
Arthur managing to provide the kick at dream stage 2, despite having less time than he thought and no gravity.
Ariadne going up a level (no, not a dream level) and deciding to take care of Mal herself.
When they cut back to her, she has this awesome look on her face that said, "Sorry, love ya, Cobb, but I've had enough of your bullshit. Time to get things done."
And flipping off Fischer's security just before he drives over the edge.
Hell, just the fact that such an example of Doing It for the Art could be made in this day and age, with Christopher Nolan holding off on filming his script for ten years until he was absolutely sure he'd ironed all the kinks out, and then receive such universal acclaim.
Saito taking out some of the invading soldiers with a grenade, despite literally being seconds away from death.
Ariadne's first journey into a dream, where she takes the road and flips half of it upside down!
Keep in mind: she has only just found out that she can manipulate the dreamworld, and her first idea is to turn half the city upside down. Girl dreams big.
In "The Cobol Job," Arthur holds up a jewelry store and makes a suicidal charge against a bunch of cops to buy time for Cobb.
A severely understated one near the end: Saito has just died and spent fifty to sixty years in Limbo. First thing he does when he wakes up is honor his promise to Cobb.
Saito's line "I bought the airline. (cue stunned looks) It... seemed neater."
When all four kicks come through: Ariadne falls off the building, then is woken up to the exploding base, which sends her to the crashing elevator, then to the truck falling down into the river, and finally back to reality (or what passes as it in this film).
A small one that most don't know: they actually dropped Ellen Page nearly 30 feet at a green-screen stage to get the shot of her leaving Limbo, when they could've just CG'd the sensation of her falling while filming her prone.
Saito's ability to actually survive limbo with his mind intact.
Fischer's utterly apathetic and deadpan reaction to being kidnapped is as awesome as it is hilarious.
"I'm insured for kidnapping for up to ten million, so this should be simple."