Is if EVER justifiable to lie?

I have to write a paper for school on whether it is ever justifiable to lie. I feel that it is only when someones life is on the line; (for example) when somebody is after you for the reason that you believe that the world should be painted purple, so your friend takes you into a hiding place, and your friend lies to the person after you that they don't know where you are, and lies to save your life. Also, if your friend lies to the cops that are after you for a crime (and you are on the death sentence) and your friend lies to the cops saying that they don't know where you are, even when they do. In this example, it would be wrong to lie, but in the first example it wouldn't. Do you see the difference? So opinions?