The ending, of course with The Bride united with her daughter at last.
The credits, even:
AKA The Bride
AKA Black Mamba
The Bride's reaction to finding out her daughter is alive is a major one too. "Overjoyed" is putting it mildly.
This exchange, after The Bride performs the Five Point Palm Exploding Heart Technique on Bill:
Bill: Pai Mei taught you...the Five Point Palm Exploding Heart Technique?
The Bride:(tearfully) 'Course he did.
Bill: Why didn't you tell me?
The Bride: I don't know...because I'm a bad person.
Bill:(tenderly) No. You're not a bad person. You're a terrific person. You're my favorite person. But every once in a while, you can be a real cunt.(The Bride laughs and cries; he wipes blood from his mouth and sits up straighter) How do I look?
The Bride:You look ready.(Bill stands up, takes six steps, collapses and dies)
The inscription on Budd's sword: "To My Brother Budd, The Only Man I Ever Loved - Bill"
Budd has two moments in this film which show that, even though he acts tough and indifferent to his big brother Bill, he still loved him. The first example being the sword that Bill gave him as a present; we see that he kept it all along, he just lied to Bill to make him cringe over the thought of hawking a priceless Hattori Hanzo sword for a mere $250. The second example is shown when he's about to bury the Bride alive via Texas Funeral. He didn't smirk, he didn't make any smartass remark...he just looked at her solemnly and said...
"Oh, and for the record, letting someone think that someone they love is dead when they're not is quite cruel."
When O-Ren begs The Bride for forgiveness for having ridiculed her swordsmanship. Forgiveness The Bride generously grants, before they resume their duel to death.
During the Bride's training montage flashback, she's trying to eat with broken hands, and drops her chopsticks to use her hands. Pai Mei throws her food away in punishment - but then pushes his own meal across the table for her to eat. Pai Mei may be a cruel and relentless master, but he still cares.
Which makes the later revelation that the Bride was his best and most favored student nothing but d'aww