I have to jump in here and mention, considering this is a subject dear to my heart, that the subject of this post is ironically incorrect. Apostrophes are possessive (and contractions), not plural. It should be Grammar Nazis, not Nazi's.
(Unless, of course as I realized AFTER I posted, you're using it in the possessive manner as in Corner of the Grammar Nazi. D'oh!)
Effect is what happens when you have an affect on something. Effect is the result, affect the action.
There - a place, their - belongs to them, they're - contraction of "they are".