In "Over My Dead Body" when Kate starts to hit on Caleb:
Kate: That is a very handsome suit.
Caleb: And that is a very pretty dress. (Beat) But it gives you back fat.
The Naked Truth from the TV series gives us several.
After the Liars find out that Kate was the one that sent that racy photo of herself in order to make Hanna look bad and get everyone to pity her, even going as far as photoshopping her head onto an attractive body,which turned out to be the dead-givaway in the end, the Liars actually manage to outwit Kate by getting her to confess, secretly recording the conversation, and showing the principle the truth.
Subsequently, we get this:
Hanna's Mother:(Clearly in reference to how Kate's mother was angrily accusing Hanna of something she didn't do) Before you go pointing fingers, you should take a look at the rotten fruit under your family tree.
Kate's Mother:(Looks at Kate, clearly disappointed.)
Another good one from this episode: Early on in the Truth Telling Exercise, Jenna asks why she should forgive the people who've bullied her at school and when Veronica asks her how she's been mistreated, Jenna quips "How much time do you have?" and begins talking about the time she was cornered and attacked in the girl's locker room, painting the scene in a way that makes her seem like the victim. Veronica asks if she ever reported it and Caleb chimes in that if she did, she'd have to admit that she threw the first punch. He then asks "Are we supposed to tell the whole truth, or just the part we want to remember?" Seeing him put Jenna in her place like that was very satisfying.
Hanna openly calling Mona out on how she hasn't changed in Mona-Mania.
Hanna slapping Jenna dead in the face.
Detective Wilden threatens Hanna if she doesn't keep quiet about his secret. Ashley's response? She rams her car into him. Lessson learned: Do NOT threaten Ashley's daughter!
Spender finding Toby's number in A's lair and using it to contact him.
Ezra refusing to let Noel blackmail him when the latter finds out about his relationship with Aria
It's a little sad to watch Emily and Spencer fight, but Emily calling out Spencer on her occasional Spoiled Brat attitude qualifies as this:
Emily: I wasn't leading him on. I was being charming. Spencer: Could have fooled me. Emily: You wouldn't know the difference. You've never had to be charming. You get to act like a total snot rag because Mommy and Daddy have a safety net of cash to catch your fall.
A little less awesome as of "EscApe From New York", when we learn that the Red Coat in question (CeCe Drake) was actually acting as a diversion so that Alison could go save Emily without A catching on. In other words, she wasn't really Aria's enemy.
However, Aria makes up for it by taking out Shana, who was prepared to kill the other girls.