Tara. I never watched a lot of Buffy but from what I remember, that's how the whole "Jossed" thing got started. Also, Fred on "Angel" was pretty f'ed up. They do it in Dr. Horrible also, at the end w/ Felicia Day's character.
EDIT: Kitty Pryde in his Astonishing X-Men run could also be included, even though they're bringing her back now.