While we're on the subject of Megatron: Beast Wars Megatron. The hammiest ham of a line of hams, bonus ham point for his English voice actor who takes ham to its apex. I remember that show from my childhood, fondly to this day, and he was a great villain. He had every vice, a perfectly twisted voice and smile, and was a T-Rex!
On the subject of Beast Wars, does Dinobot count? He's technically both villain and hero, and probably the most memorable character in the show.
Ahh kid's shows, how I miss your breed. Today's kid's shows aren't even for kids.