I mean, I was always proud of guys like Jaegren Lern--the One Living Man--and the illithid mastermind of the Saltmarsh invasion, Xil'ti'Carn. These were creatures that the PCs could really get behind and genuinely hate. And that hate? It's a powerful motivator.
Fred, in his GMing debut, really hit home with his villainous portrayal a few campaigns ago. My old swordmage-artificer Unsere was absolutely paranoid about her boss, Kezar Uzariza, and the corporation he had at his disposal. Kezar always seemed to show up at the most inconvenient times, providing a constant threat of menace that she had to overcome. For a character who was, in essence, a pacifist (at least in terms of humanoids!), this made for high drama.
I've been pleased so far, in Chris II's game, with his portrayal of Nynerin--an NPC from Keep on the Shadowfell that normally would fall by the wayside. As a fellow Valenar, Cyrid absolutely loathes everything that Nynerin pulled, particularly leading numerous villagers into the deathtrap of the titular Keep.
D&D, more than any other game, has always had its classic villains. From the demilich Acererak, to Lord Strahd von Zarovich, to the death knight Lord Soth (a personal fave!), enemies abound!
And, y'know? That's really what drives the campaign.
When I was in Liverpool, studying abroad, my professor for "Chaucer's Narrative Verse" once said something incredibly insightful. He told us, as students, that at the root of all great literature is conflict. After all,
"what would King Lear be like if everyone just sat around saying 'Pass the Cornflakes'?
So tell me, oh devoted few? What are your favorite villains? What makes them so magnetic for you? And, if you're a gamer, how do you carry that into your games?