My top 5 watched scenes would have to be:
1) "You have to be with the person you love," speech from New Moon Rising. I'm kind of from the Jane Austin school of romanticism - show all the build up to the relationship, then pull away at the crucial point, and leave it up to the minds of the audience. Probably a contravertial view point...
2) The touchy-knee bit in "Where the Wild Things Are". Your heart's in your mouth, when Willow finally plucks up the courage to touch her, and then your heart's ripped out when Tara pulls away. You're so happy when Willow's comforting her later, when Tara says she doesn't like the way the house "feels".
3) The bit where Willow is explaining why she hasn't introduced Tara to the scoobies yet, because she wants to keep her to herself. Where Tara says, "I am you know, yours."