Traps, Puzzles, Riddles and Dungeon Design: The Central Thread

[Kane0]

Trapception
The idea is that you must spring a trap in order to bypass another trap further on. For instance triggering a classic rolling boulder that chases the party down the hall or a compressing pair of walls is linked to a much larger mechanism that opens up another room. If you disable the trap that room cannot be accessed or requires additional resources to get to.
For example,
Going down a corridor there is a pressure plate (pretty easy to find), linked to a spike trap that extends blades at various points along the corridor at irregular intervals and times. Triggering this also unlocks the door at the end of the corridor, but disabling the trap breaks the locking mechanism and the door must then be forced open. Bypassing the trap means the door is still locked, and unlocking the door also springs the trap it is connected to.
For extra lethality, have some kind of guardian in the room beyond that will engage the party if they attempt to force the door.
Simple to set up, simple to put into and use in a game.

Deja vu
The idea here is that there is a whole bunch of rooms relatively near each other with only minor differences between them. Have them be thematically appropriate but each room has one or two little things out of the ordinary. If these oddities are tinkered with they will either set off a trap, open a secret area, uncover hidden loot, etc. On top of this there is a possibility the party may become disoriented if all the rooms are more or less identical unless they are well prepared and know how to find their way. For extra points use a little magic to make it more involving

A little too easy
The premise is a maze made from invisible wall of X spells. When you enter the room it looks more or less bare and you see exit(s) on other walls. Walking straight towards them is rather difficult as you keep getting stopped or affected by the wall of X spells. Detecting Magic will pretty much light up the entire room like a christmas tree and seeing invisibility or true sight will show you the maze (though not the way through it).
The party will have to expend resources to bypass/remove the maze or waste time trying to navigate it.
Bonus points for including other invisible spells like web, grease, black tentacles, etc that make going through the maze annoying but not lethal. maybe even have some paths 'discouraged' by walls of fire that can be walked through and other paths open but longer or dead ends.

Note: Seeing as most parties are very capable and D&D offers so many means of doing things it would probably be easier for you as a DM to design traps and such with the purpose of slowing down the party and fighting them via attrition rather than deterring them or stopping them entirely. Also more fun for the party that way, though make sure to have a nasty killer trap somewhere if they get too cocky.