Heh ,heh. This is great stuff. I've been collecting ideas like this for a few years, here are some good ones, none of which are mine

some of which I've gotten from other people posting here on ENWorld

.
37. A teleporting arch that the PC's must wear the evil cleric's robes to go through. If they go through wearing the robes, no problem. If they don't, they get teleported someplace naughty (like the top of a 60' deep pit filled halfway with green slime, and anti-magic runes).
38. Room is filled to a 2-inch depth with flammable oil. Room is also filled to a 1" depth with marbles. Works well in large, open rooms with balconies for mooks to shoot flaming arrows at PCs. Add chandeliers with smoke mephits for candles for additional entertainment.
39. Replace ye old metal pit spikes with wooden ones... each containing a rot grub.
40. Superglue Door. The entire surface of this door is covered with a spell that immediately causes any organic material that comes into contact with it to stick... permanently.
41. Spike-filled pit trap that is actually a stone/iron golem. Once someone falls in, the lid slams shut, and the pit/golem rises up out of the floor to attack the rest of the party. The victim in the pit/golem takes damage each round from being thrown about and onto the spikes. If it's an iron golem, lightning damages the victim inside, fire acts as a heat metal spell (lasting 1 round/die of damage), cold as a chill metal. Victim will also run out of air eventually.
42. 20-foot long pit filled with water and a wooden bridge that spans the entire pit. Unfortunately, the center 5' section was missing so a mimic came along and connected the span. PC crosses bridge. PC sticks to mimic. PC and mimic fall into water and sink. Escaping from the mimic, fairly easy. Doing so before you invoke the drowning rules, a lot tougher.
43. If you don't have a pit trap with a locking lid that drops invaders into a pit filled by a piranha swarm modified to thrive in acid instead of water, you really can't call yourself much of an evil wizard. For extra fun, pump in a heavy poisonous gas that will sit just on top of the water, where the victims' heads will be when they're trying to breathe/scream.
44. If a Wizard lives in an underground volcanic area spread rumors of his cold lair. Illusions will help too and miscellaneous spells to make the complex seem like an ice prison. Then, when they are far enough inside, they realize their mistake. They've prepared all these fire spells and whatnot to fight against the cold creature, but they then realize that their spells have no effect against defenders immune to fire. This shouldn't be done too often, of course, but try to make sure that everyone believes the exact opposite of what the Tower is truly like.
45. Iron golems standing inside walls of fire.
46. Fill the bottom of a chasm/moat with gazillions of skeletons - to pin down and murder anyone who survives the drop. Better still, place illusionary terrain above them to hide them from sight.
47. Antimagic fields over mechanical traps - everyone hates those and it's all the better to mess up rival wizards.
48. Lie about what you're up to. Paladins and priests bothering you? Tell them that while they're fiddling around with their current quest that you've razed their temple to the ground to get back at them for messing with you. Wizard? Killed their mentor. Barbarian? Killed their tribe. If they ever press for details just project a mocking smugness back like you know everything and you just aren’t telling. Lie about how you're coming to get them. Make it sound like you're mocking them because you get off on scaring your prey before you strike yada yada yada. Let them get all worked up and ready for a fight. Then you just never show up. Do this a couple times until they start realizing you're crying wolf... then when they let their guard slip, strike. Drag off one of their number in the middle of the night without alerting anyone. Or let them wake up next to a calling card of yours that lets them know you can get to them anytime you want. Lie about your goals. You fools will never stop me in time. The sacrifice will happen at midnight and there's nothing you can do to stop me. Then, when they're planning to rush in at midnight, perform the sacrifice at around suppertime. Lie through your teeth about how you're always in their mind watching, listening, and that every single plan they make they hand to you on a silver platter. Lie about your resources. If you have 50 troops, tell them their assault is doomed to failure against your army of 500 and your cabal of blood mages. Make it seem like you're just gloating when you're in fact spreading misinformation. Lie about your personal power. Claim that you can't be killed without the shattering the Stone of Cortuga, which holds safe your fell essence and that you've hidden it where nobody could find, mwa ha ha. There is, of course, no Stone of Cortuga and never was. Definitely mix it up some. Particularly when they start to catch on that you're lying. If they expect the truth, lie. If they expect a lie, feed them the most horrible truth you can as payment for their hubris. Worse, make them think that your atrocities are their fault. They doubt you killed that village? Teleport to one, kill the residents, and let them wake up the next morning with a chain of children's severed hands hanging from each of their tents. Then telepathically gift them with the memories of you doing it.
49. Bother them when they're asleep, particular the spellcasters. Wake them up. Disrupt their rest.
50. In an adverture from the book of lairs, the PCs find an empty roadside Inn, and exploring it, willquickly find several bodies drained of blood. . There are also rooms hung with garlic and holy symbols. Even if they sleep surrounded by Holy symbols, when they wake in the morning have an NPC dead of blood loss

. There is no undead, only a Slithering Tracker feeding on the PCs.
51. Plain old assassins. No confidence trick lark, just a good high-level wizard who teleports in while they're asleep and blasts the hell out of them. Or the simple high-level rogue who creeps into their room at night and slits their throats in bed.
52. Hostages. Take family members/friends hostage. Have the PCs forced to meet in a 'convenient' spot, and lay down their arms. Of course, it's a trap.
53. Corrupt Officials. Have them be attacked by some watchmen for various crimes and then try to get themselves out. Or they can attack, but then they face the whole guard establishment.
54. Animate some mouse skeletons. Strapped a caltrop onto each mouse spine. Poison it. They were directed to run under anyone's feet that came near. They use a touch attack, often on a surprise round.
55. A Rust Monster with Improved Invisibility cast on it can cause outright terror in the players, if not the characters.
56. Link some areas of a lair with underwater corridors (stairs down into water on one end, stairs up out of the water on the other end). Undead are not inconvenienced by getting wet, if they can walk out. Parties without Water Breathing available now need extra time to explore the complex- extra time to be ambushed.