Top Ten Villainous Moments in Comics

That was a pretty good list. Most stories I could think of were on it. Cosmicspidey brought up a few more. I have some as well:

When Bucky is killed by Red Skull in early Marvel Comicdom.

Joker also had another moment at the end of No Man's Land when he killed Gordon's significant other. But this pales compared to Barbara, so it shouldn't be high on the list.

Stryfe unleashing the Legacy Virus at the end of Executioner's Song. That had huge ramifications such as the deaths of Illyana Rasputin, Moira McTaggert, and Colossus (for a while).

Hyperion breaking Magik's neck in Exiles and slaughtering his team.

When Red Skull had the cosmic cube, he was a real bastard. Not a moment per say, but evil none the less.

When Hal Jordan killed Kilowog. Up until then, he had killed nameless GL's nobody cared about (oddly G'nort wasn't one of them) but when he murdered the awesome Kilowog, that was the point of no turning back to me.

When it was revealed that Riddler was behind the Hush storyline, it really restored a lot of his credibility... especially after Jim Carrey's over-the-top goofy performance made him a joke.