Firstly I ask you to forgive me for excluding the wonderful episode "Passions"... had this been a list of 20, it would have definitely been included, but as it is, it had to be the first major casualty from this list. Besides, I don't think anyone could argue how important this scene was for the show. Buffy realizes that, although she loved Angel, Angel has effectively died and there is no getting him back. Angelus is here to stay and there is very little Buffy can do about it, especially considering she has to save the world from Angelus, who plans on bringing about the apocalypse, and using his blood to suck earth into hell. She confronts Angelus with the help of the soulless vampire Spike (an important turning point for his character) but he manages to start the process which will result in the apocalypse anyway. Buffy then engages in perhaps the best one on one battle the show included, a sword fight between the ex lovers where Buffy learns a great deal about herself and the Slayer strength. When Angelus almost plunges a sword through her face by trying to emotional damage Buffy, Buffy realizes that she has the strength inside of herself to just shake off Angelus devious manipulations. Managing to fight him back, almost ready to plunge a mystical sword into his chest that will stop the apocalypse and send him to hell, Willow (from her hospital bed) manages to re soul Angelus at the worst possible moment. Angel wakes up, no longer an evil vampire and both Buffy and Angel share one last kiss, before Buffy realizes what has to be done... and in order to save the world, she effectively kills her one true love.