Here is one of my top 2 villains, the Green Goblin! This drawing is a copy of an amazing Alex Ross work you can see HERE.
The amount of stuff the Green Goblin (as Norman Osborn and Harry Osborn) is amazing. Some of the earlier stories were so ground breaking, but with how often comic book continuity is shifted around its hard to take it seriously. But to me the Green Goblin will always be one of my top 2 villains and top 5 comic book characters.
I recommend reading Amazing Spider-man #39-40, #121-122 and Spectacular Spider-man #200.