I liked Oberyn's champion speech to Tyrion.
Pretty much anything with Jaqen Hagar but particularly when Arya gives him his own name. "Un-name me!" "No" "PLEASE"
Here's probably the most dangerous character we've seen on the show begging a little girl not to make him kill himself. I thought that was funny..
The Red Wedding was memorable, although I hated everything about it.
Joffrey's death. **** that douche. I'm still waiting on Cersei to get hers..