Two favourites. First from TSFS -
Kirk: My God Bones, what have I done?
Bones: You did what you had to do, what you've always done. Turn death into a fighting chance to live.
And from TWOK
"Of all the souls I have encountered, his was the most human." It's not the line so much as the way Shatner delivers it, the way he chokes up as he says human.