9. Ben Reilly (Scarlet Spider) - Peter Parker: Spider-Man #75
There was no way that someone was going to come in and permanently replace Peter Parker as Spider-Man without raising the hackles of more than a few fans - which was exactly the case for the unfortunate Ben Reilly, who became the questionably received Scarlet Spider.
Reilly himself had his fans, boasting a brilliant design both as the Scarlet Spider and when he became Spider-Man full time, but no fan preferred him to Peter. Entangled in a web of convoluted plot-twists and awkward character moments, Marvel then made the decision to kill Reilly off, having the Green Goblin attach the man to a missile, and then send it flying towards Spider-Man.
When Peter dodges the human missile, it leaves Ben careening to his death off the side of a building, and Spider-Man with yet another tragic death to add to his list of trauma.
While Reilly would be revived for the 'Dead No More' storyline, this still left him dead and gone for a considerable part of time - possibly to ensure that when he came back, it wouldn't be to an audience that were still freshly salty over the Clone Saga storyline that tried to replace Spider-Man in the first place.