Extremism in the defense of liberty?

I've been thinking about various political labels and the recent spate of harsh political rhetoric. It seems that both the Left and Right often label their opponents as extremists. Yet I am wondering what the truth is to this. Which positions really are extremist as opposed to simply being conservative or liberal? Of course some conservatives would say that any liberal position is extremist by its very nature and vice versa for liberals. But I disagree with this, as I'm guessing many of you would.

So, I'd like to open up the comments for submissions of truly extremist positions. Please give some thought to this; I'm not looking for attacks against either side. I'm looking for some reasoned thought on what are truly extremist positions.