A few things I've done or seen since posting in this thread originally:
Anthropomancy: In a lawless pirate city dedicated to an evil god, the PCs needed some clues on where to find evidence of a mounting army of undead. Locals recommended going to a diviner for help in finding stuff. The diviner was a little girl who lived on the edge of town. She was cute: blond pigtails, pink dress, cherubic smile... and solid black, "shark eyes." Also: turns out she'd been divining for this town for more than fifty years.
She told them that her divination method required a dying man's entrails; did they have anyone in their group they were willing to sacrifice? No... but one character snuck out at night, went to the slave market, bought the weediest, sickest, (and cheapest) little gnome or halfling he could find, and took him to the little girl. With her arms elbow deep in the gnome's innards as he croaked out his death rattle, she gave that character a number of actually quite useful tips.
This all happened between sessions. When it became obvious to the other players that what he had done... priceless.
The Eye Thief. I had a weird little fey creature that was invisible most of the time, but who could be seen in mirrors. He turned up one night while the PCs were sleeping in an inn... he had attacked a young NPC woman in her room and scooped out her eyes with a spoon. Of course; they couldn't see him, and couldn't figure out what had happened exactly, so they went uneasily back to bed. Then, it tried to attack one of the PCs in her room.
It actually was pretty easy to defeat, as it turned out, due to some really good luck, but they were pretty seriously creeped out by that little blighter.
To top it all off, one of the PCs made some kind of Knowledge roll, and figured that if the eyes were recovered from the little fey (who popped stolen eyes into his own sockets) and if a remove blindness spell were cast with the eyes back again, you'd actually have
improved vision and the ability to see invisibility sometimes. One character volunteered to take the poor young woman out to get healed. When he comes back, his formerly brown eyes are now green...
Accidentally sold your soul. After defeating a few really creepy demon-dogs (no Thundarr jokes, please) who had a breath weapon of... yep, you guessed it... maggots, the bodies melted and coalesced into a demonic princess. She was trying to assume a humanoid form, but it had been so long since she'd seen one that she didn't quite get it right. Too many eyes... too many breasts... her... nether regions had long needle-like teeth and a long, barbed, slurping tongue that hung to her knees. She took one look at the female PCs and adjusted her form, becoming the most painfully beautiful woman imaginable. Then she healed the party for them, including the womanizing swashbuckler who was in negative hit points and thus had missed her introduction. He immediately leapt into action, promising to be at her service. She accepted their offer to become her emmissaries and disappeared.
I guess that's really more great roleplaying than creepiness, but the aghast looks and "WHAT HAVE YOU DONE?!" dialogue was truly priceless.
