[Nejat Sari]

First time I played I freaked out when the medallion started vibrating during sex with Adda. Shani's party was just... great. And I'm a sucker for conversations like the one with Triss in Act V, where they talk about settling down and building a house, and Geralt playing homemade bagpipes.

But gotta say that my favourite scene is the end of the prologue on a second playthrough (because by then I knew the witchers' place in the world, how they are the last of a dying breed). After Vesemir tells you that they're abandoning Kaer Morhen, then burning Leo's body, and the goodbye with Triss afterwards, it's like the witchers' swan song: beautiful and tragic.

[nihilio]

The noonwraith video on chapter 4 had me gazing at the beauty of it.
The Party was my favourite quest.
As for dialogue, I think it is the conversation with De Wett in chapter 5, where

he is gentle and civil, but ends with a "fuck you!" that is such a great example of great writing

[Schmooples]

Saving all hostages in Murky Waters and getting Vapors of the Hunt.

EDIT: Oh yeah, and the con artist, I put him to Zeugl's food after he reveals he tricked me.

[Treasa]

I cried at the presentation of Aerondight and at Leo's funeral, but the defining moment when I knew I loved this game was when Zoltan and Geralt had the philosophy lesson in chapter 2.

[Gilrond]

I liked the Aerondight and knighting of Geralt scene the most.

[mariobros777]

The moment of using dagon's altar and the invasion of the deep ones. Oh, geralt getting knighted, the lady of the lake, her ash that puts others to shame, and all that stuff. Stuff of legend, really! Finally and most importantly, his obligation bestowed upon him, to speak truth at all times, follow his destiny and be true or something (do not remember exactly that specific speech from the lady, but that is which i mean).