Buffy/Angel- The whole of 'I Will Remember You' is slushy, gooey, romantic mush and I love it.
Buffy/Spike- I always like the scene in 'Fool For Love' where he goes to kill her with his shotgun, but he see's she's upset and in pain. He just sits with her on the steps and offers what comfort he can. Nice and understated.
Buffy'Riley- Um, Guilt free sex. lots of it, that's gotta count for something, right?
Willow/Kennedy- I guess I can think of worse rebound relationships, also it confirmed Willow's 'new' orientation. But I prefer the snake-chick from the comics, to be honest.
Gunn/Fred- They weren't right for each other, but they were really sweet and romantic together.