I voted for Yuki vs Asakura, since I nominated it.
Everything in this scene was perfect, the animation is so fluent, the music fits the situation perfectly, and you get to know Yuki better.
Asakura was kind of creepy in a positive way too.
As great as the blackmail scene is, Haruhi talks to Kyon really defines what the show is all about.
I vote for Haruhi Blackmail! It is a memorable scene and it's definitely the one that draws people in most when they first start the series! ;)
When being served something as sweet and delicious as cake, it's not having the cake that's important. It's the enjoyment of eating that cake that's important, and it's more enjoyable when done with a friend.