Okay, so it's not a musical mashup, but this is such a near-seamless mixing with such care and attention to detail that I had to share it. Besides, with Twilight: Eclipse opening to the hysterical shrieking of middle-aged women with too many cats and too much disposable income across the country, I couldn't resist.
Buffy/Edward - Twilight Remixed
(Incidentally: There has been some discussion within my social group, and the consensus is that, forced to choose a "team," we'd all definitely go "Team the Guy Who Has a Tan and Body Heat and, Oh Yeah, Shape-shifts into a Freaking Wolf." That said, otherwise, we're all firmly on Team Buffy.)