General

The Riddler & Mr Freeze

Monsieur Mallah and The Brain

Flagg...the planes-walking demon. He's honestly the scariest thing to ever be created by Stephen King, bar none. Practically Satan, but all sarcastic wit and dark humor.

The Riddler, so wonderfully eccentric and fun.

Carnage, a homicidal, sadistic, psychopath. WITH superpowers. I find most villains are just tragic people with misguided views or goals, not Carnage though, he's pure evil. :O

Megatron, because no one can be a bad guy quite like him.

Darkseid, Anton Arcane, Daleks, The Master, and Venom

Yura...of the Hair.

My sister and I frequently chuckle about her. But she was definitely a legitimately creepy villain.

Ooh, yes, he's awesome!

Still alive...

T-1000, metal shapeshifting pointy killing awesomenessssss

If I had to cast my vote it would be G-man from the Half-Life Series. He's creepy, powerful, enigmatic, and ever Half Life I first came out, we still don't know what his motives are, who or what he is, or who he works for. The fact that on every level he is "somewhere" just watching you always gave me the heebie jeebies. If I had to say a close second it would Kane from Command And Conquer. Although his actions are largely misunderstood, they lead to a world filled with greater dystopia.