For me, it was while we were both slightly drunk, sat on a bench eating chips, she said "You know I love you, dont you". She had never said it to me before, although I had no trouble being able to tell her, and she just said it like it was a normal sentence. I really melted inside when she said it.

Second place has to be when I finally confessed how I felt to her before we started going out, and she simply said "kiss me".