There are way too many... some have already been mentioned...
"After a time, you may find that having is not so pleasing a thing, after all, as wanting. It is not logical, but it is often true."
Some heartbreaking lines:
Spock's entire speech after he breaks down in
The Naked Time
"For the first time in my life, I was happy" in
This Side of Paradise
"Computers make excellent and efficient servants, but I have no wish to serve under them. Captain, a starship also runs on loyalty to one man. And nothing can replace it or him." Love the quiet, dignified way he says it, after being teased about prefering computers to people throughout the episode.
Endearing and unintentionally funny on his part: Spock talking about tribbles while stroking them in TTWT;
also, I love the way he says "That 'unit' is a woman!" in
The Changeling. So often it is in the delivery and context.
For sarcasm, many of his retorts to McCoy... but I LOLed particularly ain The Trouble with Tribbles, when he corrects Chekov:
Kirk: Mr. Chekov, this flight is supposed to provide both experience and knowledge. How close will we come to the nearest Klingon outpost if we continue on our present course?
Chekov: Ah, one parsec, sir. Close enough to smell them!
Spock: That is illogical, Ensign. Odors cannot travel through the vacuum of space.
Chekov: I was making a little joke, sir.
Spock: Extremely little, Ensign.
In "Miri": "Ah. It seems that being a red-blooded human has its disadvantages."
But often his raised eyebrow is even funnier than any lines.
I love the way he answers when someone notices he's lied:
"A lie."
"An omission."
"You lied! "
"I exaggerated."
"You lied."
"I implied."
"If I were human, I believe my response would be: 'go to hell'. If I were human."
"Since my customary farewell would appear oddly self-serving, I shall simply say: Good luck."
ZQ's Spock had some great Spocky moments: "Out of the chair" ;
"I have no comment on the matter";
and of course, "Live long and prosper" delivered as it was, was something else.
High five, Possum. You have good taste. Spock's facial expression when he says that is priceless.
SO corny! It almost ruined that episode for me, which till that point I thought was great (though in a campy way). I hate seeing the big 3 do that really lame baby talk, but McCoy's interaction with Julie Newmar throughout the rest of the episode was hilarious and as I stated earlier, I loved Spock's final words.
