How about a little turnabout?
A summoned monster is dispelled when it hits 0 hit points, right? It doesn't die, but is returned to its natural environment. How about an NPC with a wand of summoning that picks the PCs as the "summoned monster"? The PCs get epic combats that by all rights should kill them, and you get the chance to do a little "destructive testing" on them, but when it's all over, they wake up 24 hours later.... All the fun of a TPK without the fistfight afterwards. (Complications: Make the NPC's alignment congruent with or diametrically opposed to the PCs, so either they have to diplomatically get him to stop using it (when they finally track him down), or they are compulsed to fight good creatures.)
Maybe a trap that splits the party, and they have to continue seperately? Especially handy if it takes only the spellcasters.
A player doesn't show up, and in the first combat/trap/whatever, his character gets knocked out cold. Not only do the others have to go on without him, but they have to carry and care for his comatose body.
When I really want to take the wind out of the PCs sails, I use Kobolds. They never fight unless they have the advantage, and use poison, traps, ambushes, low ceilings, difficult terrain, and mobility to harry their enemies. And their preferred class is Sorcerer. My best ambush yet was Kobold crossbowmen with Spider Venom poison (1d4 Str), and a Sorcerer with Web and Spider Swarm. Lesser Sorcerers had Magic Missile, Ray of Enfeeblement, and Touch of Fatigue. The one character with Escape Artist (and any chance of escaping the web) kept failing his nausea check from the Spider Swarm.
Other ways to mess with the party are obvious clues that don't mean a damned thing. An early D&D module had a ring of mushrooms growing in a circle around a fireplace in an abandoned house. There was a loose stone in the fireplace, and other loose stones had coughed up treasure before. The party took 15 minutes figuring out how to handle the situation, but the mushrooms were perfectly normal.
Telas