i have a few but my favorite was when meredith told gary clark to shoot her in the finale...It was a very meredith grey move and her speech blew me away. Actually that whole scene was amazing. I almost died when derek "died".
My favorite was when Meredith and Derek go to the brunch after Valentine's Day and the sign says "Dr. and Mrs. Shepherd" then after the brunch Meredith and Derek are driving home and Meredith is like " Mrs. Shepherd!! I do not do brunches or Valentine's Day" And then she says to Derek "you are going to have to make this up to me with lots of sex" and Derek says "Yes Dear" I think that is the absolute best scene in the whole season.
The whole finale...Meredith telling Cristina she´s pregnant, "going through" her to get to Derek and kneeling beside him on a catwalk, her "shoot me" speech, Bailey in every scene and especially Cristina operating with gun to her head