Ratings are out of a possible five bulbs of garlic.

Bill Compton, True Blood. While he's rather morose and generally humorless, at least he has fangs and doesn't glitter in the sunlight.
Rating: Three garlic bulbs

Claudia, Interview With The Vampire.
Forget Tom Cruise and Brad Pitt: The creepiest bloodsucker in the adaptation of the Anne Rice book was Kirsten Dunst's child monster, all curly hair and demon thoughts. Remember when she brought home the twins for Lestat, and they were poisoned? Evil!
Rating: Three garlic bulbs

Eli, Let The Right One In. You want awkward tweenage love story? You want blood? This Swedish art film delivers, beautifully. Eli is the mysterious girl-next-door; Oskar's a bullied kid who could use someone in his corner. This large-eyed little vamp is simultaneously sweet and unsettlingly menacing. (Check out the trailer here.)
Rating: Four garlic bulbs

David, The Lost Boys. Keifer Sutherland makes it look so cool. He's got chicks, a posse, and a cave hangout. He may or may not make you eat worms and drink blood — but that's the price you pay for hanging with the right crowd! Look, that's Bill, from Bill & Ted's Excellent Adventure on the far right! See how connected these vamps are?
Rating: Five garlic bulbs

Blade. So maybe he's half vampire. But Wesley Snipes was a badass VOC (that's vampire of color) with a Buddhist outlook, sharp weapons and the advantage of being a daywalker.
Rating: Three garlic bulbs

Selene, Underworld. Since she and her vamp vicious circle were so busy hunting werewolves, they weren't much of a threat to humans, and therefore not very scary. Kick ass and gorgeous, but not scary.
Rating: Two garlic bulbs

Spike, Buffy The Vampire Slayer. Many BTVS fans worshipped Angel, Buffy's brooding first love, but Spike, the devilish, quippy, smart-ass, black nail polish-wearing vamp who once said, "I may be love's bitch, but at least I'm man enough to admit it," was actually the better character. Part Billy Idol, part Bowie, part rabid dog, Spike's cuckoo mate, Drusilla, once asked him, "Do you love my insides? The parts you can’t see?" Answered Spike: "Eyeballs to entrails, my sweet!" This is how a vampire thinks: He loves you so much he may dine on you. We never quiet get that from Edward Cullen.
Rating: Four garlic bulbs

Special mentions: Laddie from The Lost Boys, The Count, Dracula, and, of course, Blacula.
Update/Addendum:

Box Office Report: 'Twilight' Sinks Its Teeth Into A Blockbuster Debut [EW]
Why Do We Love Vampires? [iVillage]
Earlier: Twilight At Midnight: Smells Like Teen Spirit
I Was A Teenage Trend-Hater: Despising Twilight Is Big For Fall
Twilight: "Questionable Casting, Wooden Acting, Laughable Dialogue And Truly Awful Makeup"
Breaking Dawn: What To Expect When You're Expecting... A Vampire