Given the well-traveled nature of this group, I figured this was the question to ask as opposed to the states that you have visited.
For the Canadians, Chileans, Aussies, etc., in the group feel free to chime in as you see fit.
Changing planes in an airport doesn't count but driving through (with or without stopping) does.
My list is as follows:
OK & TX - I hear some okay things about OK but besides Austin, the state of TX has absolutely no appeal to me.
SC - Would like to visit Charleston & the coast someday.
AK - Next on my list, hopefully.