There are too many to list. But one of my very favorites is in Ben's hut. After they watch the hologram, how Obiwan looks at Luke, then gets that gleam in his eye, and the whole movie changes.  Alec Guiness was such an incredible actor, he elevated the entire movie.

The scene in Return of the Jedi when Luke throws his lightsaber away and rejects the dark side.

And says "Never.  I'll never turn to the dark side.  You've failed your highness.  I am a Jedi, like my father before me".

When Vader says "If you will not turn to the dark side, perhaps she will" hitting Luke's soft spot.

The whole Luke hanging from Bespin is one of my faves!!

The scene where Owen says: "Well, he better have those units in the south range repaired by midday or there will be hell to pay!"

:)

Seriously, it's probably the scene when Yoda dies and Luke feels all alone with such a huge task ahead for him, and some interesting revelations.

Another great scene is when Tarkin is talking to Leia.  Peter Cushing is masterful the way he crowds her and says "I grow tired..."  nobody could have played that scene better!

The scene with the two droids bickering in the desert after crashing in the escape pod.

Here are two visually and narratively synthetic characters and yet they show more humanity than any of the 'real' people in the PT and in most dramatic representations generally.

Artoo and Threepio are people in that scene, all things considered that's astonishing.

Bingowings said:

Here are two visually and narratively synthetic characters and yet they show more humanity than any of the 'real' people in the PT and in most dramatic representations generally.

Can't say I agree with this, but whatever... To each his own.

As a kid, I loved, loved, loved the trash compactor scene.  It was such a predicament to overcome (the monster, walls closing), and it just plain looked cool.  I remember in winter I'd go in my grandmother's backyard and slosh around in a big puddle, where I'd pretend the bits of ice floating on the surface were like the garbage floating in the water.

Nowadays, I'd say my favourite scene is a toss up between Ben looking over at Luke in ANH just before Vader kills him, or (and I hate admitting this) the scenes in ROTS where Anakin and Padme stare across the city at each other with only the Brian Eno-ish music playing, or Obi-Wan saying to Padme, "Anakin is the father, isn't he?... I'm so sorry," just before he leaves to go kill Anakin.

Puggo - Jar Jar's Yoda said:

Another great scene is when Tarkin is talking to Leia.  Peter Cushing is masterful the way he crowds her and says "I grow tired..."  nobody could have played that scene better!

Yes! It's really too bad they killed Tarkin off so soon. I'd love to have seen Peter Cushing through the entire trilogy.

I have a fondness for the scene in ROTJ where Luke grabs his new lightsaber out of the air and activates it; first time I saw a lightsaber that wasn't blue or red, and I loved it!

Too bad Windu's purple saber didn't elicit similar feelings when I first saw it; I suppose the idea of a relatively minor, peripheral character being the only character to get a unique lightsaber in the films just irked me >:-(

I don't understand the shame either...