[scottevill]

I think it's pretty clear it was Xander. When Willow's giving her whole speech about knowing that someone in the room is in love with Buffy, even if they don't want to admit it to themselves, and that person has to just suck it up and kiss her -- while everyone else closes their eyes on pain of *losing* them -- it culminates on a close-up of Xander, where she just says, "OK?"

In the next panel, Buffy is sitting up, awake. Had to be Xander. (Besides, we know he's been in love with her all this time--They just de-emphasized that plot many seasons ago.)