When Luke ignites his new lightsaber after escaping his execution. Always has me grinning stupidly.
Or the moment right before that where it is made clear, via a combination of body langauge and camera cues, that the heroes are about to put their plan into action.
Flying into the Death Star is crazy enough, but then the Tie Fighters come in after them as well.
During the Battle of Endor, Green Leader aka Arvel Crynyd's fighter gets shot down. As his ship begins to break apart, the pilot manages to crash it clean through the bridge of the Executor, causing it to lose all control and smash into the Death Star. Best. Death. Ever.
Not only that, but according to Expanded Universe, after the battle there was an award named after the pilot called the Crynyd Award, given for conspicuous bravery in space combat.
The Rebels also named a captured Star Destroyer after the guy.
Watching the Executor, a ship so large it literally overshadowed the Star Destroyers from The Empire Strikes Back, get destroyed by plummeting into the Death Star, with the crew of Ackbar's ship cheering triumphantly.
Before that, there's the scene where while Ackbar's telling the fleet to concentrate firepower on the Executor, if you look out ahead there's a normal Star Destroyer exploding in the distance. It's like Lucas wants to show us what a Star Destroyer looks like being destroyed before showing us the destruction of the Executor.
"I am a Jedi, like my father before me." One of the most powerful scenes in the entire series happens when Luke throws away his lightsaber following his revelation from beating Vader.
Also doubles as a Crowning Moment of Heartwarming, since it shows to Anakin/Vader that despite all he's done, his son still believes in his inner goodness.
This is made even more awesome as it's the first time that Palpatine has been really suffered a major setback, if you compile all the previous five other movies (including the prequels), throwing away those he considered useless and manipulating everyone up to that point. Luke was the first one not to be swayed by his words, and he didn't like that.
Instead of seeking cover like everyone else when Leia threatens to blow up Jabba, Boba Fett quickly picks up his blaster carbine.
After being captured by Jabba and made to wear a very revealing "bikini", Leia strangles Jabba using the same chain he was using to keep her prisoner.
Luke taking down three biker scouts during the speeder bike chase by the following methods: Jumping from the speeding bike piloted by Leia onto the back of one scout's and throwing him off. Then using that bike's blaster to shoot down another ahead of him. And then after falling off it, using his lightsaber to deflect the blasts of another oncoming scout and stepping out of the way and slicing the steering vane off his bike so it spins out of control and crashes into a tree.