While I was prepping my failed Adventure Week adventure, my gaming group and I started brainstorming traps I could use. This lead into a broader discussion on traps and tricks a GM can pull on his players. I feel bad I didn't have a recorder because it would have made a great podcast, but I'll try and compile the ideas out of that discussion and come up with some useful advice:
Think Last Crusade not Raiders
The Indiana Jones movies are both the greatest boon and the worst bane to trap design. In the climax of Last Crusade Indy (perhaps the patron saint of player characters) is given clues to defeat the dungeon's traps. Making them very dynamic puzzles, rather than the roadblock puzzles typical of dungeon design. Whereas in the opening of Raiders of the Lost Ark we see Indy use perception and deft footwork to avoid pressure-triggered dart traps. This is cool on film, but do you have any idea how that plays out in a D&D dungeon crawl:
Rogue: I search this square *roll* 17.
DM: Seems clear.
Rogue: I move on to it...carefully.
DM: Nothing springs out of the wall trying to kill you.
Rogue: Okay, I search the next one *roll* 22.
DM: Yeah, that one does trigger poison-y death.
Rogue: I attempt to disarm *roll* 14.
DM: Sure, you wedge it down enough to be safe to cross.
Imagine that for every single square of the 40 foot long hallway. You might as well just summon a tedium elemental to your table. On a related note, never place a deadly trap on a door, ever. You're just asking for thorough search of every door in your campaign.
Learn from Last Crusade, give the players clues about your dungeon's death course beforehand and grant a bonus on any saves to get through those traps if they can puzzle those clues out.
Traps as a complication
Rather than make the trap the entire obstacle, make them a set piece encounter with some lower tier enemies. A gang of low-level warriors isn't much of a threat to 6th level PCs, but add some spears popping out of the walls or a shallow spiked-pit trap and the whole thing gets a lot more interesting. As a bonus, your PCs will feel smart for turning the traps against their foes.
Another fun trick is to put a elemental-based trap in a room with a creature that is immune to (or better, is healed by) that element. Nothing breeds gaming stories like a flesh golem in a room where chain lightning hits everyone every 1d6 rounds.
Traps as a Frustration
Similar to the above example use traps to slow down or annoy players. Team up an alarm with a minor status ailment or a penalty to die rolls just to make the next encounter a pain to the incautious. One trick I like to pull is have a kobold lure the players around a corner and then spring some flimsy-barred gates in front of and behind the PCs, letting the kobold and his friends get a free round or two to pelt my players with ranged weapons while they bash down the gates.
Monsters that don't look like monsters
2nd edition D&D had a lot of monsters that looked like the environment. A DM could create a room wherein everything; floor, ceiling, walls, furniture, clothing, tree stumps is trying to kill you. Animated objects are great for this, as are stone golems disguised as statues. Everyone has seen the treasure chest that is in fact a mimic trick, but that's for console RPGs. Mimics can mimic anything up to a certain size, get creative, mimic writing desks, mimic weapon racks ("Did the weapon rack just smack me with a glaive?"). My favourite disguised monster trick is to have an elemental lying in wait for players: water elementals posing a puddles, fire elementals lurking in braziers, that unassuming pile of rock is an earth elemental. True story, I had a group of epic level characters get in a fight with a lake.
You could also try traps that aren't really traps. One of the most frustrating puzzles I've ever encountered as a player was what looked like a magic missle trap that couldn't be disarmed was actually a wand-equipped apprentice wizard running around a secret passage parallel to the main hall tossing magic missles out of holes in the walls.
Use illusions cover blatantly obvious pits and rock falls so that players blunder into them without so much as a second thought. More fun is to invert the idea; place illusions of obvious danger over harmless terrain to obfuscate players. Use triggered image spells to make players think they're being attacked by monsters and waste resources. Building an elaborate death course with spinning blades, flamethrowers, smashers, and trap doors is an expensive prospect for the busy evil overlord on the go, but creating a illusion of that death course gives you a very similar effect for a fraction of the cost.
Mix and Match from the Above
Use illusions to cover simple pits in the middle in of a mook encounter, combine a puzzle-trap with a frustration. Go nuts, it'll drive your players crazy.
Apologies if this advice comes off as D&D-centric, but the conversation was with my Pathfinder group. Most of these ideas should convert to most genres with some re-imagining.