A few I can watch again and again:

-- The scene at the beginning of GFII, where Connie goes in to talk to Mike. His sheer disgust with Connie in that scene is astounding. "Why do you come to me, why don't you go to a travel agent?"; "YOU'RE NOT MY FATHER," "Then what do you come to me for?!" "Because I need money!" And when he asks (or tells her) to leave Merle, and he says "Now he'll understand, believe me."

-- I agree with many above, any scene with Michael V. Gazzo.

-- The flashback scene when Vito murdered Don Ciccio. He doesn't settle for just stabbing him, he runs the knife all the way up his stomach. Then the way he just pushes his head away, like he's nothing. A truly powerful moment. A Don rising in power in America, avenging his family, and murdering the most powerful Don in Sicily.

-- The baptism scene, of course.

--The shooting during the Lake Tahoe scene. I, too, continuously look for the culprit(s) in that scene.

-- The "Hail Mary" scene in GFII

-- The shooting of Don Corleone in GF. He falls so slowly, in just agony. And the look on Fredo's face. Yes, Brando was awesome in that scene, but I think Cazale stole it.

-- Speaking of Cazale, I think he gives Gazzo a run for his money in [i]GFII{/i]. The boathouse scene is probably my favorite scene in the whole trilogy. You can't help but feel sorry for Fredo, you can't help but loathe Michael in that scene. I've seen it probably a thousand times, but everytime I watch it, I find myself saying "Please Michael, just let it go. He's your brother."

So many more to mention, not enough time...