Here are some of my favourites, the ones that come to my mind right now.
a) Original RE1. Chris is trying to play the piano, Rebecca comes in.
Rebecca: "It's me, Chris!"
Chris: "Is that YOU, Rebecca?"

Makes me think: "No, I'm not Rebecca, I'm Becky Radames, a doppelgänger that looks exactly like Rebecca, and my job is to kill you and then take over the world!"
b) Remake. Chris confronts Wesker in the laboratory alone. Wesker turns around, fights him to the ground and puts a foot on his chest... So erotic!

Especially when Chris is wearing his street costume, his eyes are hidden behind sunglasses and his mouth opens a little when Wesker puts the gun in his face... Chris looks like he's truly enjoying it.
c) RE2. Ada saves Leon from Mister X in the power room and still keeps on shooting him in the face while he's hurling her around by the neck. Incredibly badass, Ada! I also like the alternate scene when Mister X confronts Sherry in the same room and she throws her pendant to Claire, who then throws it into the pool of molten iron.
d) Nemesis. How Jill flies out of that building in the beginning, how she flees from the exploding gas station, and the whole train crash thing.
e) Code Veronica. Alfred loses his wig. Honestly, who would have expected
that? This turn of events has made him one of my favourite villains.
f) Code Veronica again. The fight between Chris and Alexia. Alexia thinks of everyone as worker ants who live only to support her, the queen, who turns into something that looks like a dragonfly. Then she is killed by Chris, an
ant, just like she and her brother killed a dragonfly in the past by letting it be eaten alive by ants. Although I would have liked it better if Claire had been the one to kill Alexia, and Chris had killed Alfred instead. Siblings fight!!
g) RE5. Wesker is about to fall out of the plane, grabs Sheva's leg, she lets go, slow motion, Chris remembers how he lost Jill... and then grabs her. Perfect rhetoric! If you then go back to the flashback scene about Jill's "death", you can regard it as a foreshadowing of what will eventually happen to Chris's new partner too, but then he will be able to prevent it.