From the Storm:

Aang: I???m going to find them.
Katara: I???m going with you.
Old Woman: I???m staying here

Ty Lee: You Are NOT Prettier than we are. (To the Kyoshi Warriors)

Appa's Lost Days

Toph: I am the greatest earthbender in the world and don't you forget it!

Or something like that.....

Zuko: I don't want to make a life here! (speaking??to Uncle Iroh at his suggestion to Zuko about having a??lady-friend over to their apartment in Ba??Sing Se)

Iroh: Life happens wherever you are, whether you make it or not.

(so true, so true)

goodjob everyone

My favorites are:

Zuko: I know you're scared and I know you're not ready to save the world, but if you don't defeat the Fire Lord before the comet comes there won't be a world to save anymore.

Aang: No I'm not gonna end it this way. Ozi: Even with all the power in the world you're still weak.

Katara: Do you need anything? Aang: I need to redeem myself. I need my honor back.

Uncle Iroh: You need to start looking inward and start asking yourself the big questions. Who are you and what do you want?

Katara: I thought you had changed!
Zuko: I have changed.

I don't know what it is about that exchange, but I think it's quite chilling. Maybe it's the way Zuko responds coldly or the fact that he responds coldly whilst fighting.

Azula to Dai Lee Agents: If I sense any disloyalty, any hesitation, any weakness at all.... I will snuff it out [glares at the Dai Lee agent in front].

Katara to Zuko: Oh, everyone trusts you now? I was the first person to trust you, remember, back in Ba Sing Se, and you turned around and betrayed me. Betrayed all of us.