Any main character.
Dany or her manservant
Robb, Arya or Sansa
Lady Stark, and now Brienne
The cripple or his wildling nanny
Jamie or Cersei
Tyrion or Shae
Jon Snow, and now his girlfriend
The whoremonger and the eunach
The Hound or Bronn
I’m really not feeling like any of those people could be killed off at any point, but rather that they are going to live because they are main characters and just like any other story, you don’t kill off the main characters.
On the cusp would be Stannis, Renly and Drogo, and two of those did actually die so maybe there have been more major deaths than I’m giving credit for.
Did Renly feel like a main character to any of the non-book readers? To me he seemed very much like a bit part, but thinking back on season one we did spend a fair amount of time with him.
While Joffrey is a main character, he’s a classic bad guy so I wouldn’t count him in the breathless praise for how ruthless the author is for killing beloved characters. I’ll be surprised if Joffrey lives, to be honest. I tend to think of Drogo in the same category. Jaime and Cersei would be in this group but those two are really quite major roles so that would be pretty ruthless.