@Liberty: Thanks for the suggestion. I didn't list him because I think he's been overused. I got tired of him a long time ago, even though he's an important Captain America foe. That's just me.
@caesarsghost: Thanks! Joker is iconic but honestly I am tired of him. That's just me. Captain Cold, for whatever reason, has always appealed to me. Thanks for commenting!
@Decept-O: Good list, but some of these characters just don't seem that bad to me! Last time I checked, they were either anti-heroes, or just misunderstood!
@infonation: I totally agree. For example, John Jameson. Not really a "bad guy" per se, but because initially he was a "villain" to Spider-Man as Man-Wolf I decided to list him as such. Villains can often be misunderstood depending on the story, so yeah, that is true. Thanks for checking this out and commenting.