There are soooo many, but the first one that comes to mind - Clemenza's basement; Clemenza is "instructing" Mike on the how to dispatch Sol and McC. I love the set, the working man's basement. It's a serious moment that turns whimsical when Michael comments about the noise of the gun, "madonne, my ears", but then Clemenza shows his soft side, his affection for Mike, "you know we was all proud of you, even your father." The look on Clemenza's face, perfect show of emotion.