My friend has a picture of himself after smoking 1 joint of Strawberry Diesel... Needless to say, he's passed out on the sofa and actually dribbling... He's also known to be quite a resilient smoker.
It's one of the hardest hitting strains I've ever smoked you feel fine one minute then about 10minutes after you've finished smoking, it's like you've been given a local anaesthetic in your legs, neck and arms. It's just impossible to keep moving on that stuff. Couch lock is an understatement, I think completely bludgeoned to death would be adequate.
A few more which I would have to think twice before rejecting would be... Durban Poison, White Rhino, Lemon Kush, California Orange and Bubblegum.
However, I feel that this thread is flawed and we should be able to pick two strains! One for taste and one for the high, that way we get some variety and we don't get bored of what we're smoking!