OH YEAH I TOTALLY LOVE THIS TOPIC.
Prepare yourselves, for you are about to witness the ultimate villain fangirl known to mankind.
1. Judge Claude Frollo, from Disney's Hunchback of Notre Dame.
Arguably Disney's darkest and most threatening villain, Judge Claude Frollo embodies everything a villain should be - ruthless, insane, sadistic, held to a twisted set of iron-clad morals, and full of lust. His desire for the gypsy woman Esmeralda is turning his religious nature on its ear, and he blames God for not destroying her. While his insanity begins to ravage him as his burning lust for Esmeralda grows higher and higher, he delivers possibly the best Disney Villain song: Hellfire. This is not, like most Disney villain songs, a song about how evil he is. It's a song about how he's tormented by what he believes is Satan's minion, Esmeralda, and wants her to either be his mistress or burn in hell.
Disney. You know, for kids!
2. The Joker and Harley Quinn from Batman: The Animated Series.
The Joker is the ultimate comic book villain, both on screen, on paper, and in our heads. He's funny, but he's also sick. His dark sense of humor makes us wonder if we're going to hell for laughing at his jokes. When he needs to be, he's sly and charming, and can play us for fools any day of the week. At the same time, he loves chaos and torture, and - like Frollo - has a sense of twisted morals in regards to his nemesis, Batman. Even at his most charming there's no sense of humanity in him, and when he turns into his overpowering monster, all of us get the chills.
And then there's Harley. Oh my gosh, there's Harley. The last person in the world in need of a sidekick would be the Joker, and yet for him, it flat out works. She's just as sick, determined, humorous and obsessed as he is, and their relationship is both deranged, beautiful, and tragic at the same time. Clad in skintight leotard, she's both beautiful, incredibly dangerous, and would die for the Joker. Actually, he does try to kill her a few times. Their relationship can be picked apart and analyzed over, but I love them. They're villainous romance at it's best - dark, horrible, funny, and abusive.
3. Syndrome, from The Incredibles.
He's the Joker without being fully realized. He's quite dark, and very much a little boy at heart - his whole reason for villainy stemmed from a bad experience as a little boy. But where the Joker has a sense of humor about his crimes and almost reveres Batman as being the Yin to his Yang, Syndrome is virtually humorless except when confronted with the pain and anguish of his once-icon, Mr. Incredible. He's the darkest kind of hero-fanboy, and behind that buck-toothed grin and wild orange hair, there's a little boy lurking in those baby blue eyes. That's possibly what makes him so effective - that our hero, the man we're cheering for, created his own villain.
4. Dr. Facilier, The Princess and the Frog
Does he even need an introduction? Charming as the devil himself, the good Doctor can manipulate you into any corner he wants with just a wink of those purple eyes. He's dangerous when up against a wall though, and has possibly the best shadow ever put onscreen. I love how he effortlessly twists people's dreams back on themselves, truly teaching the lesson of what you want may not be what you need. While his voodoo magic is mysterious, frightening, and downright bizarre, there's no doubt that he can use you as his puppet any day of the week.
5. Vector, Despicable Me.
Er, hilarious. Yes. Downright hilarious, with a perfect character design and some truly hysterical moments. He also has the added bonus of being from my second favorite animated film of all time. <3 Despicable Me is rare in that every single character design is perfect for that character and voice, and Vector is no exception. Vector is what every pimpled nerd wants to be - they want to be the richest supervillain of all time, with awesome weapons like the Squid Launcher! Oh yeah! Okay, maybe that's just me. But still, Vector is funny, determined, and above all, the geekiest supervillain you'll ever meet.
Honorable Mentions: (Villains I like but can't be bothered to post pictures/explain why they're awesome.)
John Silver, Treasure Planet.
Ursula, The Little Mermaid.
Rasputin, Anastasia.
Prince Charming and the Fairy Godmother, Shrek II.
Queen of Hearts, Alice in Wonderland.