Which Trek scene has the best moral building speech you can recall, for me it's DS-9 ep "Favor the Bold" scene when after a mission Sisko is with the crew and The Chief brings in a spent Phaser Coil. I don't recall Sisko's exact wording, but he states that this spent coil represents more than just some spent equipment, it represents the fight in the Defient and in the Federation, later in the same ep Jadzia gives more of less the same speech, and the chief puts the coil in a line of spent coils...
Re: Moral Building... It'd have to be one of Kirk's - there's the ever famous "Risk is our business," of course, but I'm even more fond of his address to the crew after Balok scares the bejezus out of them in "The Corbomite Maneuver." It works because he's not speechifying so much as just talking - focused but almost conversational in tone - and it's not all bombast and oratorical generalities, but reassures people and calls them back to their duty in a crisis by reminding them of who they are and what they know to be true.
Re: Moral Building... If he had given that talk in later seasons, it would have been filled with bombast.
"I'm going to ask all of you to think back to the day when this ship was first launched. We were explorers then. When all this is over, when Earth is safe, I want you to get back to that job. There are four hundred billion stars in our galaxy, we've only explored a tiny fraction. You have a lot of work to do. Of all the captains who will sit in this chair, I can't imagine any of them being more proud than I am right now." --- Captain Archer, before going on his suicide mission to Azati Prime
When Damar made his speech calling on the Cardassian people to rise up against the Dominion. This came just after the Federation alliance had just seen Earth attacked and they had lost a major battle, so Damar provided a ray of hope and became their only chance to save the Alpha Quadrant.