I'm gonna agree that Buffy and Spike and Wes and Lilah were set-the-world-on-fire hot. I mean, seriously. They were Brian-and-Justin hot, which is pretty much the tippy top of my hotness scale. There is a definite reason for which most of you have voted for one or both of these pairings.
I've got to give props to my man Giles nailing Joyce on the cop car, too. I mean... gah! Twice. In a row, apparently. And with handcuffs. Dude. Does it get any hotter than that? Sadly, it was off screen. But from the few details to which we are privy, we know that it involved public sex, bondage, the flouting of authority, and multiple performances. I mean, dag on. I am drooling, here. It sounds like it was too hot to show on screen. lol.
I'm also partial to any possible combination of the fanged four, with special notice going to Spike & Dru. That was one screwed up little family, but man did the pheromones seem to fly whenever they were in a scene together! That scene in Fool for Love -- the one in which they're walking through the flaming carnage of the Boxer Rebellion -- just sort of screams depraved sexiness. I am certain beyond a doubt that those four had some incredibly wild nights.