Moiraine's testing in the White Tower! When New spring was released I thought this was the only moment that contributes somehow to the main story.A major thing that was not described in the main series. For everything else in NS we had some hints.

And my opinion hasn't changed.The significance of this moment is not depreciated by Nyn's testing ToM. The latter was not a waste of pages either - the contrast between these two events is stunning.

Second close come her words to Thom: "Tanchico will not kill you" thus outplaying him as rand's adviser and turning on the red light in my head for the upcoming romance

I don't know if her "post mortem" letters should be accounted for her moments as she is off-screen when those are being read. If so, these two would grab the top spots.