Our favorite Billy Idol look-alike goes from a one-dimensional vampire badass to one of Buffy the Vampire Slayer's most dynamic characters. He enters the scene, out for Buffy's blood like any other respectable demon in Sunnydale, but ends up falling in love with her. Because of this, he seeks redemption and a soul — which he manages to get. Oh, then he saves the world from Ubervamps. So, yay Spike!
Best bad-boy line: "What can I tell you baby? I've always been bad."