Great question!I have a few examples.
For Xander: The troll episode (I'm not so good with the titles) where he is supposed to choose who lives between Willow and Anya. He doesn't, and procedes to get his hand broken and his ass kicked, and not only does he not choose, but over and over he goes back for more, without even hesitating.
Also at the end of Family when he tells Tara's brother he will break something if he tries to beat Tara. I think he was referring to the breaking that he, Xander would do, not just Buffy.
And how about bringing Buffy back to life the first time in Prophecy Girl? He was all heroic with the CPR.
For Willow: I agree about the episode where she chooses to stay in Sunnydale with Buffy and fight the good fight.
Also, the scene near the end of Season 3 where she faces of with Faith after Faith catches her reading. There is the infamous "Well BOO HOO" line that I always loved. She tells Faith that she should feel lucky to have someone like Buffy in her life, but instead she threw Buffy and all the other scoobies away. Definately one of her finest hours, IMO.
Another biggie is when she took control of the situation in The Weight of the World when all the scoobs were fighting. She broke up Spike and Xander, gave everyone a task, and then went into Buffy's mind to save her.
Tara: When Tara goes outside and comforts Dawn early in season 5 when the body is in the magic box, and she thumb wrestles her. Tara is Dawn's hero starting here, and then over and over.
There is also her series of interactions with Anya in Bargaining 1 and 2. She saves Anya from the biker who was riding off with her. She also yanked her into the bushes to hide her, and then comforted her at the magic box. Then she sent out tiny tinkerbell light to lead Willow and Xander back to town. She has a quiet bravery that really shines through. And of course, who could forget the ax? Nobody messes with her girl.
Giles: When he stood up for Tara at the end of Family. He knew Tara had cast a spell on them, but forgave her. He also sensed that Mr. Maclay was not going to pay heed to Buffy and Dawn being that they were woman, and he very obviously stepped in as the "Man" and stood up to Mr. Maclay.
I think killing Ben was definately another moment for Giles. I think he did it to spare Buffy from having to do so. He knew it would kill her. Ironic, no?
Anya: When she whacked the Byzantine knight with the frying pan in Spiral, and fought him off of Tara and Dawn.
Also when she tried to save Dawn early in Real Me, when Harmony kidnapped her. She got her arm broken or sprained or something, but still tried to save her.
I have more, but I'll stop for now. Love this thread!
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"You're in my blood like Holy Wine
You taste so bitter, and so sweet
Darling, I could drink a case of you
And still be on my feet;
I would still be on my feet."
-Joni Mitchell