Here's a few I picked up various places, some right here on EN World.
Capture your foe and chain him within a bog standard dungeon after taking a lock of his hair. Take 12 hours to create a simulacrum. Parade said simulacrum in front of your prisoner, then order it to go be a good father and husband to your prisoner's family. Wheel an enchanted mirror in front of the prisoner's cage so he can watch the simulacrum spend time with his family, play with the children, make love to his wife, everything he should be doing. Beat or starve the prisoner to taste, and when he starts to act up, threaten to have the simulacrum murder his family. Maybe, from time to time, give the simulacrum orders and make him watch as it carries them out. A special, romantic dinner with his wife. Teaching his son how to fish, and screaming at him whenever he makes a mistake. Just little things to twist the knife. For double the fun, don't let the simulacrum know it's a simulacrum. Just use modify memory, etc. Hopefully, some day you can reveal the truth to the simulacrum, letting it know that it is just a worthless puppet you created for your own amusement. Hopefully the realization will destroy the simulacrum mentally. Maybe it'll even kill itself. Then the original gets to watch in escalating horror as the family grieves over the dead clone.
Inappropriate section excised. Please pay attention to our 'Grandma' rule.
Have monsters fight from behind cover, and put a pit trap of some sort along the path to the monsters cover. Players like to charge into melee, and they tend to get dumped right into the pit. If your really mean, the pit will be filled with water, to a depth of 8 feet or so, and have a heavy iron grate drop onto the pit and fall into place just below the surface of the water. A 50 pound iron grate is hard to lift when your feet are not on the ground. And since it is a grate, you can have humanoids with spears stab past the grate at the guy under it. The water is there just to help the guy drown.
And then there's of course the much-feared Wandering Little Girl. The PC's are camped for the night in the middle of monster infested wilderness, leagues from any civilization. Out of nowhere walks a little girl to their camp and sits by the fire. She says nothing and does nothing but warms her tiny hands for a moment before setting off again. If they attack, they kill it with a single attack and you can scold them for killing an innocent mute child who was lost and searched for a moment of rest. If they do nothing, you will never reveal what it was and what was it doing there, keeping them in wondering what the heck was it for years to come.
IF you really want to mess with them, run a one off session where the players discover something suspicious. Lets say that a few families die of plague, their homes are cleaned out by the church, but neighbors mention that the children of the family aren’t among the dead, and have gone missing. When they ask around, tell them that a priest was seen with the child a few nights before the child died. Also mention that the same thing happened a few other times. When the players bust their way into the church and discover, to their horror, a well-run orphanage/day care, run by loving and caring people. The children were removed from the home to keep them from getting sick.
This one I did to a couple PCs once, it was gold, as the celestial almost died
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.
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.
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.
Invest in Ghasts. Pits with Ghasts in them, silent, waiting. Pits with water in them, and a Ghast underwater at the bottom waiting to drag them under. Know what happens to paralyzed air-breathing creatures underwater?
A Ghast with a Pebble of Silence can do fearsome damage if all the characters attempt to disbelieve rather than counter the Pebble.